Method for channel access in wireless communication system and apparatus for performing same

ABSTRACT

A method for performing channel access in an unlicensed band by a base station in a wireless communication system according to an embodiment of the present invention may comprise the steps of: sensing, in an unlicensed band, a carrier for transmitting a downlink signal; and transmitting the downlink signal when power detected by sensing the carrier is less than an energy detection threshold set by the base station, wherein the energy detection threshold is set to be equal to or less than a maximum energy detection threshold determined by the base station, and when another radio access technology (RAT) sharing the carrier exists, the maximum energy detection threshold is adaptively determined depending on the bandwidth size of the carrier, using the value, in decibels, of the ration between a reference bandwidth and the bandwidth of the carrier.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of performing channel access in awireless communication system supporting an unlicensed band and anapparatus therefor.

BACKGROUND ART

A 3rd generation partnership project long term evolution (3GPP LTE)(hereinafter, referred to as ‘LTE’) communication system which is anexample of a wireless communication system to which the presentinvention can be applied will be described in brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a wireless communication system. The E-UMTS is an evolved version ofthe conventional UMTS, and its basic standardization is in progressunder the 3rd Generation Partnership Project (3GPP). The E-UMTS may bereferred to as a Long Term Evolution (LTE) system. Details of thetechnical specifications of the UMTS and E-UMTS may be understood withreference to Release 7 and Release 8 of “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), basestations (eNode B; eNB), and an Access Gateway (AG) which is located atan end of a network (E-UTRAN) and connected to an external network. Thebase stations may simultaneously transmit multiple data streams for abroadcast service, a multicast service and/or a unicast service.

One or more cells exist for one base station. One cell is set to one ofbandwidths of 1.44, 3, 5, 10, 15 and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify the correspondinguser equipment of time and frequency domains to which data will betransmitted and information related to encoding, data size, and hybridautomatic repeat and request (HARQ). Also, the base station transmitsuplink (UL) scheduling information of uplink data to the correspondinguser equipment to notify the corresponding user equipment of time andfrequency domains that can be used by the corresponding user equipment,and information related to encoding, data size, and HARQ. An interfacefor transmitting user traffic or control traffic may be used between thebase stations. A Core Network (CN) may include the AG and a network nodeor the like for user registration of the user equipment. The AG managesmobility of the user equipment on a Tracking Area (TA) basis, whereinone TA includes a plurality of cells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology will be required for competitivenessin the future. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure andopen type interface, proper power consumption of the user equipment,etc. are required.

DISCLOSURE OF THE INVENTION Technical Task

A technical task of the present invention is to provide a method of moreprecisely and efficiently performing CCA (clear channel assessment) whena transmission node performs channel access on an unlicensed band celloperating on the basis of LAA (licensed-assisted access) and anapparatus therefor.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

In an aspect of the present invention, a method of performing channelaccess by a base station on an unlicensed band in a wirelesscommunication system, includes sensing a carrier of an unlicensed bandfor transmitting a downlink signal, and transmitting the downlink signalwhen power detected by sensing the carrier is less than an energydetection threshold that is configured by the base station. The energydetection threshold can be configured to be equal to or less than amaximum energy detection threshold determined by the base station. Whena different radio access technology (RAT) sharing the carrier is able toexist, the maximum energy detection threshold can be determinedadaptively to a bandwidth of the carrier using a decibel value of aratio between a reference bandwidth and the bandwidth of the carrier.

In another aspect of the present invention, a base station performingchannel access on an unlicensed band includes a processor to sense acarrier of an unlicensed band for transmitting a downlink signal, and atransmitter to transmit the downlink signal when power detected bysensing the carrier is less than an energy detection threshold that isconfigured by the base station. The energy detection threshold can beconfigured to be equal to or less than a maximum energy detectionthreshold determined by the base station. When a different radio accesstechnology (RAT) sharing the carrier is able to exist, the maximumenergy detection threshold can be determined adaptively to a bandwidthof the carrier using a decibel value of a ratio between a referencebandwidth and the bandwidth of the carrier.

Preferably, the maximum energy detection threshold can be configured tobe equal to or greater than a first power value which is a sume a lowerbound of the maximum energy detection threshold for the referencebandwidth and the decibel value.

And, the first power value is obtained by a first equation ‘−72+10*log10(BWMHz/20 MHz) [dBm]’, ‘20 MHz’ of the first equation corresponds tothe reference bandwidth, ‘BWMHz’ corresponds to the bandwidth of thecarrier represented in a unit of MHz, ‘10*log 10(BWMHz/20 MHz)’corresponds to the decibel value, and ‘−72’ may correspond to the lowerbound of the maximum energy detection threshold for the referencebandwidth represented in a unit of dBm.

And, the maximum energy detection threshold can be configured to beequal to or greater than a second power value which is determined inconsideration of a difference between the decibel value and maximumtransmit power of the base station set for the carrier.

And, the second power value is obtained by a second equation‘min{T_(max), T_(max)−T_(A)+(P_(H)+10*log 10 (BWMHz/20 MHz)−P_(TX))}[dBm]’, ‘T_(max)’ of the second equation corresponds to ‘10*log10(3.16288*10⁻⁸/BWMHz)’, ‘T_(A)’ corresponds to a constant predefinedaccording to a type of the downlink signal, ‘P_(H)’ corresponds to 23dBm, ‘20 MHz’ corresponds to the reference bandwidth, ‘BWMHz’corresponds to the bandwidth of the carrier represented in a unit ofMHz, ‘10*log 10(BWMHz/20 MHz)’ corresponds to the decibel value, and‘P_(TX)’ may correspond to the maximum transmit power of the basestation set for the carrier.

And, the maximum energy detection threshold can be determined to be agreater value among the first power value obtained by adding the decibelvalue to −72 dBm and the second power value.

And, when the downlink signal includes physical downlink shared channel(PDSCH), the ‘T_(A)’ can be configured by 10 dB and when the downlinksignal includes a discovery signal but does not include the PDSCH, the‘T_(A)’ can be configured by 5 dB.

When the different RAT sharing the carrier does not exist, the maximumenergy detection threshold may not exceed T_(max)+10 dB.

The downlink signal is transmitted via at least one licensed-assistedaccess secondary cell (LAA SCell) operating based on LAA and the sensedcarrier may correspond to a carrier at which the at least one LAA SCellresides.

Advantageous Effects

According to one embodiment of the present invention, when atransmission node performs channel access on a carrier of an unlicensedband, since a maximum value of an energy detection threshold forperforming CCA is configured adaptively to a bandwidth of a carrier anda change of transmit power, it is able to more precisely and efficientlyperform the CCA in various wireless channel environments.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic diagram of E-UMTS network structure as one exampleof a wireless communication system;

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard;

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels;

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system;

FIG. 5 is a diagram for an example of a resource grid for a downlinkslot;

FIG. 6 is a diagram illustrating a structure of a downlink radio frameused in an LTE system;

FIG. 7 is a diagram illustrating a structure of an uplink subframe usedin an LTE system;

FIG. 8 illustrates a UL HARQ operation in LTE system;

FIG. 9 is a diagram for explaining FDD system and DL/UL HARQ timeline;

FIG. 10 illustrates scheduling in a case that a plurality of carriersare aggregated;

FIG. 11 illustrates a UL HARQ operation in LTE system;

FIG. 12 is a diagram for explaining FDD system and DL/UL HARQ timeline;

FIG. 13 is a diagram for an example of a method of using an unlicensedband;

FIGS. 14 and 15 illustrate a FBE operation;

FIGS. 16 and 17 illustrate am LBE operation;

FIG. 18 is a flowchart for explaining a method of configuring a maximumvalue of an energy detection threshold according to one embodiment ofthe present invention;

FIG. 19 a flowchart for a method of performing channel access accordingto one embodiment of the present invention;

FIG. 20 is a diagram illustrating a base station and a user equipmentapplicable to embodiments of the present invention.

MODE FOR INVENTION

The following technology may be used for various wireless accesstechnologies such as CDMA (code division multiple access), FDMA(frequency division multiple access), TDMA (time division multipleaccess), OFDMA (orthogonal frequency division multiple access), andSC-FDMA (single carrier frequency division multiple access). The CDMAmay be implemented by the radio technology such as UTRA (universalterrestrial radio access) or CDMA2000. The TDMA may be implemented bythe radio technology such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by the radio technologysuch as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of a universal mobiletelecommunications system (UMTS). A 3rd generation partnership projectlong term evolution (3GPP LTE) is a part of an evolved UMTS (E-UMTS)that uses E-UTRA, and adopts OFDMA in a downlink and SC-FDMA in anuplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

For clarification of the description, although the following embodimentswill be described based on the 3GPP LTE/LTE-A, it is to be understoodthat the technical spirits of the present invention are not limited tothe 3GPP LTE/LTE-A. Also, specific terminologies hereinafter used in theembodiments of the present invention are provided to assistunderstanding of the present invention, and various modifications may bemade in the specific terminologies within the range that they do notdepart from technical spirits of the present invention.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard. The controlplane means a passageway where control messages are transmitted, whereinthe control messages are used by the user equipment and the network tomanage call. The user plane means a passageway where data generated inan application layer, for example, voice data or Internet packet dataare transmitted.

A physical layer as the first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a medium access control (MAC) layer via a transportchannel, wherein the medium access control layer is located above thephysical layer. Data are transferred between the medium access controllayer and the physical layer via the transport channel. Data aretransferred between one physical layer of a transmitting side and theother physical layer of a receiving side via the physical channel. Thephysical channel uses time and frequency as radio resources. In moredetail, the physical channel is modulated in accordance with anorthogonal frequency division multiple access (OFDMA) scheme in adownlink, and is modulated in accordance with a single carrier frequencydivision multiple access (SC-FDMA) scheme in an uplink.

A medium access control (MAC) layer of the second layer provides aservice to a radio link control (RLC) layer above the MAC layer via alogical channel. The RLC layer of the second layer supports reliabledata transmission. The RLC layer may be implemented as a functionalblock inside the MAC layer. In order to effectively transmit data usingIP packets such as IPv4 or IPv6 within a radio interface having a narrowbandwidth, a packet data convergence protocol (PDCP) layer of the secondlayer performs header compression to reduce the size of unnecessarycontrol information.

A radio resource control (RRC) layer located on the lowest part of thethird layer is defined in the control plane only. The RRC layer isassociated with configuration, re-configuration and release of radiobearers (‘RBs’) to be in charge of controlling the logical, transportand physical channels. In this case, the RB means a service provided bythe second layer for the data transfer between the user equipment andthe network. To this end, the RRC layers of the user equipment and thenetwork exchange RRC message with each other. If the RRC layer of theuser equipment is RRC connected with the RRC layer of the network, theuser equipment is in an RRC connected mode. If not so, the userequipment is in an RRC idle mode. A non-access stratum (NAS) layerlocated above the RRC layer performs functions such as sessionmanagement and mobility management.

One cell constituting a base station eNB is set to one of bandwidths of1.4, 3.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to several user equipments. At this time, differentcells may be set to provide different bandwidths.

As downlink transport channels carrying data from the network to theuser equipment, there are provided a broadcast channel (BCH) carryingsystem information, a paging channel (PCH) carrying paging message, anda downlink shared channel (SCH) carrying user traffic or controlmessages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted via the downlink SCH or anadditional downlink multicast channel (MCH). Meanwhile, as uplinktransport channels carrying data from the user equipment to the network,there are provided a random access channel (RACH) carrying an initialcontrol message and an uplink shared channel (UL-SCH) carrying usertraffic or control message. As logical channels located above thetransport channels and mapped with the transport channels, there areprovided a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels.

The user equipment performs initial cell search such as synchronizingwith the base station when it newly enters a cell or the power is turnedon at step S301. To this end, the user equipment synchronizes with thebase station by receiving a primary synchronization channel (P-SCH) anda secondary synchronization channel (S-SCH) from the base station, andacquires information such as cell ID, etc. Afterwards, the userequipment may acquire broadcast information within the cell by receivinga physical broadcast channel (PBCH) from the base station. Meanwhile,the user equipment may identify a downlink channel status by receiving adownlink reference signal (DL RS) at the initial cell search step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH at stepS302.

Afterwards, the user equipment may perform a random access procedure(RACH) such as steps S303 to S306 to complete access to the basestation. To this end, the user equipment may transmit a preamble througha physical random access channel (PRACH) (S303), and may receive aresponse message to the preamble through the PDCCH and the PDSCHcorresponding to the PDCCH (S304). In case of a contention based RACH,the user equipment may perform a contention resolution procedure such astransmission (S305) of additional physical random access channel andreception (S306) of the physical downlink control channel and thephysical downlink shared channel corresponding to the physical downlinkcontrol channel.

The user equipment which has performed the aforementioned steps mayreceive the physical downlink control channel (PDCCH)/physical downlinkshared channel (PDSCH) (S307) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S308), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station willbe referred to as uplink control information (UCI). The UCI includesHARQ ACK/NACK (Hybrid Automatic Repeat and reQuestAcknowledgement/Negative-ACK), SR (Scheduling Request), CSI (ChannelState Information), etc. In this specification, the HARQ ACK/NACK willbe referred to as HARQ-ACK or ACK/NACK (A/N). The HARQ-ACK includes atleast one of positive ACK (simply, referred to as ACK), negative ACK(NACK), DTX and NACK/DTX. The CSI includes CQI (Channel QualityIndicator), PMI (Precoding Matrix Indicator), RI (Rank Indication), etc.Although the UCI is generally transmitted through the PUCCH, it may betransmitted through the PUSCH if control information and traffic datashould be transmitted at the same time. Also, the user equipment maynon-periodically transmit the UCI through the PUSCH in accordance withrequest/command of the network.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 4, in a cellular OFDM radio packet communicationsystem, uplink/downlink data packet transmission is performed in a unitof subframe, wherein one subframe is defined by a given time intervalthat includes a plurality of OFDM symbols. The 3GPP LTE standardsupports a type 1 radio frame structure applicable to frequency divisionduplex (FDD) and a type 2 radio frame structure applicable to timedivision duplex (TDD).

FIG. 4(a) is a diagram illustrating a structure of a type 1 radio frame.The downlink radio frame includes 10 subframes, each of which includestwo slots in a time domain. A time required to transmit one subframewill be referred to as a transmission time interval (TTI). For example,one subframe may have a length of 1 ms, and one slot may have a lengthof 0.5 ms. One slot includes a plurality of OFDM symbols in a timedomain and a plurality of resource blocks (RB) in a frequency domain.Since the 3GPP LTE system uses OFDM in a downlink, OFDM symbolsrepresent one symbol interval. The OFDM symbol may be referred to asSC-FDMA symbol or symbol interval. The resource block (RB) as a resourceallocation unit may include a plurality of continuous subcarriers in oneslot.

The number of OFDM symbols included in one slot may be varied dependingon configuration of a cyclic prefix (CP). Examples of the CP include anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be 7. If the OFDM symbols are configured by the extended CP,since the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is smaller than that of OFDM symbols incase of the normal CP. For example, in case of the extended CP, thenumber of OFDM symbols included in one slot may be 6. If a channel stateis unstable like the case where the user equipment moves at high speed,the extended CP may be used to reduce inter-symbol interference.

If the normal CP is used, since one slot includes seven OFDM symbols,one subframe includes 14 OFDM symbols. At this time, first maximum threeOFDM symbols of each subframe may be allocated to a physical downlinkcontrol channel (PDCCH), and the other OFDM symbols may be allocated toa physical downlink shared channel (PDSCH).

FIG. 4(b) is a diagram illustrating a structure of a type 2 radio frame.The type 2 radio frame includes two half frames, each of which includesfour general subframes, which include two slots, and a special subframewhich includes a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS).

In the special subframe, the DwPTS is used for initial cell search,synchronization or channel estimation at the user equipment. The UpPTSis used for channel estimation at the base station and uplinktransmission synchronization of the user equipment. In other words, theDwPTS is used for downlink transmission, whereas the UpPTS is used foruplink transmission. Especially, the UpPTS is used for PRACH preamble orSRS transmission. Also, the guard period is to remove interferenceoccurring in the uplink due to multipath delay of downlink signalsbetween the uplink and the downlink.

Configuration of the special subframe is defined in the current 3GPPstandard document as illustrated in Table 1 below. Table 1 illustratesthe DwPTS and the UpPTS in case of T_(s)=1/(15000×2048), and the otherregion is configured for the guard period.

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended Special subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

In the meantime, the structure of the type 2 radio frame, that is,uplink/downlink configuration (UL/DL configuration) in the TDD system isas illustrated in Table 2 below.

TABLE 2 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

In the above Table 2, D means the downlink subframe, U means the uplinksubframe, and S means the special subframe. Also, Table 2 alsoillustrates a downlink-uplink switching period in the uplink/downlinksubframe configuration of each system.

TABLE 3 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, — — — — — — — 7, 5, 4, 11, 6 6 — — 7 7 5 — —7 7 —

Table 3 illustrates UL ACK/NACK timeline. If a user equipment receivesPDCCH and PDSCH scheduled by the PDCCH in a subframe #(n-k), itindicates that UL ACK/NACK is transmitted in a subframe #n in responseto the received PDSCH.

And, the ACK/NACK for the PDSCH is transmitted on PUCCH corresponding toa UL control channel. In this case, information transmitted through thePUCCH may vary depending on a format. It is summarized as follows.

In LTE system, a PUCCH resource for ACK/NACK is not allocated to each UEin advance. Instead, a plurality of UEs belonging to a cell use aplurality of PUCCH resources by sharing the resources at every timing.Specifically, a PUCCH resource, which is used for a UE to transmitACK/NACK, is implicitly determined based on PDCCH carrying schedulinginformation on PDSCH on which corresponding DL data is carried. In eachDL subframe, the whole region to which PDCCH is transmitted consists ofa plurality of CCEs (control channel elements) and PDCCH transmitted toa UE consists of one or more CCEs. A CCE includes a plurality of (e.g.,9) REGs (resource element groups). One REG includes 4 adjacent REs(resource elements) except a reference signal (RS). A UE transmitsACK/NACK via an implicit PUCCH resource which is induced or calculatedby a function of a specific CCE index (e.g., first or lowest CCE index)among CCE indexes constructing the PDCCH received by the UE.

In this case, each PUCCH resource index corresponds to a PUCCH resourcefor ACK/NACK. For example, if scheduling information on PDSCH istransmitted to a UE via PDCCH configured by CCE indexes 4 to 6, the UEcan transmit ACK/NACK to a BS via PUCCH, e.g., fourth PUCCH, induced orcalculated from a 4^(th) CCE index corresponding to the lowest CCE indexamong the CCEs constructing the PDCCH.

PUCCH format 1a/1b transmits A/N information, PUCCH format 2/2a/2btransmits CQI, CQI+A/N information, and PUCCH format 3 can transmitmultiple A/N information.

The structure of the aforementioned radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, or thenumber of symbols included in the slot.

FIG. 5 is a diagram of a resource grid for a downlink slot.

Referring to FIG. 5, a DL slot includes N_(symb) ^(DL) OFDM symbols intime domain and N_(RB) ^(DL) resource blocks. Since each of the resourceblocks includes N_(sc) ^(RB) subcarriers, the DL slot includes N_(RB)^(DL)×N_(sc) ^(RB) subcarriers in frequency domain. FIG. 5 shows oneexample that the DL slot includes 7 OFDM symbols and that the resourceblock includes 12 subcarriers, by which the present invention isnon-limited. For instance, the number of OFDM symbols included in the DLslot can be modified according to a length of a cyclic prefix (CP).

Each element on a resource grid is called Resource Element (RE) and 1single resource element is indicated by a single OFDM symbol index and asingle subcarrier index. A single RB is configured with N_(symb)^(DL)×N_(sc) ^(RB) resource elements. The number N_(RB) ^(DL) ofresource blocks included in the DL slot is dependent on a DLtransmission bandwidth configured in a cell.

FIG. 6 is a diagram illustrating a structure of a downlink subframe.

Referring to FIG. 6, maximum three (four) OFDM symbols located at thefront of the first slot of the subframe correspond to a control regionto which a control channel is allocated. The other OFDM symbolscorrespond to a data region to which a physical downlink shared channel(PDSCH) is allocated. Examples of downlink control channels used in theLTE system include a Physical Control Format Indicator Channel (PCFICH),a Physical Downlink Control Channel (PDCCH), and a Physical Hybrid ARQIndicator Channel (PHICH). The PCFICH is transmitted from the first OFDMsymbol of the subframe, and carries information on the number of OFDMsymbols used for transmission of the control channel within thesubframe. The PHICH carries HARQ ACK/NACK (Hybrid Automatic RepeatreQuest acknowledgement/negative-acknowledgement) signals in response touplink transmission.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a user equipment or user equipment group. Forexample, the DCI includes uplink/downlink scheduling information, uplinktransmission (Tx) power control command, etc.

The PDCCH may include transport format and resource allocationinformation of a downlink shared channel (DL-SCH), transport format andresource allocation information of an uplink shared channel (UL-SCH),paging information on a paging channel (PCH), system information on theDL-SCH, resource allocation information of upper layer control messagesuch as random access response transmitted on the PDSCH, a set oftransmission (Tx) power control commands of individual user equipments(UEs) within a random user equipment group, transmission (Tx) powercontrol command, and activity indication information of voice overInternet protocol (VoIP). A plurality of PDCCHs may be transmittedwithin the control region. The user equipment may monitor the pluralityof PDCCHs. The PDCCH is transmitted on aggregation of one or a pluralityof continuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide the PDCCH with a coding rate based onthe status of a radio channel. The CCE corresponds to a plurality ofresource element groups (REGs). The format of the PDCCH and the numberof available bits of the PDCCH are determined depending on the number ofCCEs. The base station determines a PDCCH format depending on the DCIwhich will be transmitted to the user equipment, and attaches cyclicredundancy check (CRC) to the control information. The CRC is maskedwith an identifier (for example, radio network temporary identifier(RNTI)) depending on usage of the PDCCH or owner of the PDCCH. Forexample, if the PDCCH is for a specific user equipment, the CRC may bemasked with cell-RNTI (C-RNTI) of the corresponding user equipment. Ifthe PDCCH is for a paging message, the CRC may be masked with a pagingidentifier (for example, paging-RNTI (P-RNTI)). If the PDCCH is forsystem information (in more detail, system information block (SIB)), theCRC may be masked with system information RNTI (SI-RNTI). If the PDCCHis for a random access response, the CRC may be masked with a randomaccess RNTI (RA-RNTI).

FIG. 7 is a diagram for an example of a structure of an uplink subframein LTE.

Referring to FIG. 7, an uplink subframe includes a plurality of slots(e.g., 2 slots). A slot can include the different number of SC-FDMAsymbols depending on a CP length. An uplink subframe is divided into adata region and a control region in frequency domain. The data regionincludes PUSCH and is used for transmitting a data signal such as audioand the like. The control region includes PUCCH and is used fortransmitting uplink control information (UCI). PUCCH includes an RP pairpositioned at both ends of the data region in frequency axis and hops ata slot boundary.

PUCCH can be used for transmitting control information described in thefollowing.

SR (scheduling request): Information used for requesting uplink UL-SCHresource. OOK (on-off keying) scheme is used to transmit the SR.

HARQ ACK/NACK: Response signal for a DL data packet on PDSCH. Thisinformation indicates whether or not a DL data packet is successfullyreceived. ACK/NACK 1 bit is transmitted in response to a single DLcodeword. ACK/NACK 2 bits are transmitted in response to two DLcodewords.

CSI (channel state information): Feedback information on a DL channel.CSI includes a CQI (channel quality indicator) and MIMO (multiple inputmultiple output)-related feedback information includes an RI (rankindicator), a PMI (precoding matrix indicator), a PTI (precoding typeindicator) and the like. 20 bits per subframe are used.

An amount of control information (UCI) capable of being transmitted by auser equipment in a subframe is dependent on the number of SC-FDMAsavailable for transmitting control information. The SC-FDMAs availablefor transmitting the control information correspond to the remainingSC-FDMA symbols except SC-FDMA symbols used for transmitting a referencesignal in a subframe. In case of a subframe to which an SRS (soundingreference signal) is set, a last SC-FDMA symbol of a subframe is alsoexcluded. A reference signal is used for coherent detection of PUCCH.

FIG. 8 is a diagram of a resource unit used for constructing a downlinkcontrol channel in LTE system. In particular, FIG. 8(a) indicates a casethat the number of transmitting antennas of an eNode B corresponds to 1or 2 and FIG. 8(b) indicates a case that the number of transmittingantennas of the eNode B corresponds to 4. A reference signal (RS)pattern varies according to the number of transmitting antennas but amethod of configuring a resource unit in relation to a control channelis identical irrespective of the number of transmitting antennas.

Referring to FIG. 8, a base resource unit of a downlink control channelis a REG (resource element group). The REG consists of 4 neighboringresource elements except an RS. The REG is represented in the drawingwith a bold line. The PCFICH and the PHICH include 4 REGs and 3 REGs,respectively. The PDCCH consists of a CCE (control channel element) unitand one CCE includes 9 REGs.

In order for a UE to check whether the PDCCH consisting of L number ofCCEs is transmitted to the UE, the UE is configured to check the CCEscontiguously arranged by M(^(L)) (≥L) number of CCEs or a specific rule.A value of the L, which should be considered for the UE to receive thePDCCH, may become a plural number. The UE should check CCE aggregationsto receive the PDCCH. The CCE aggregations are called a search space. Asan example, the search space is defined by LTE system as Table 4 in thefollowing.

TABLE 4 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

In this case, CCE aggregation level L indicates the number of CCEconsisting of PDCCH, S_(k) ^((L)) indicates a search space of the CCEaggregation level L and M^((L)) indicates the number of candidate PDCCHsmonitored in the search space of the aggregation level L.

The search space can be classified into a UE-specific search spaceaccessible by a specific UE only and a common search space accessible byall UEs in a cell. A UE monitors the common search space of which theCCE aggregation level corresponds to 4 and 8 and monitors theUE-specific search space of which the CCE aggregation level correspondsto 1, 2, 4, and 8. The common search space and the UE-specific searchspace may overlap with each other.

And, a position of a first (having a smallest index) CCE in a PDCCHsearch space, which is given to a random UE for each CCE aggregationlevel value, varies in every subframe depending on a user equipment.This is called a PDCCH search space hashing.

The CCE can be distributed to a system band. More specifically, aplurality of CCEs, which are logically contiguous, can be inputted to aninterleaver. The interleaver performs a function of mixing a pluralityof the CCEs with each other in REG unit. Hence, frequency/time resourcesforming a CCE are physically distributed in the total frequency/timedomain within a control region of a subframe. Consequently, although acontrol channel is constructed in a CCE unit, the interleaving isperformed in an REG unit. Hence, frequency diversity and interferencerandomization gain can be maximized.

FIG. 9 is a diagram for an example of a carrier aggregation (CA)communication system.

Referring to FIG. 9, a wider UL/DL bandwidth can be supported in amanner of aggregating a plurality of UL/DL component carriers (CC). Sucha term as a component carrier (CC) can be replaced with a differentequivalent term (e.g., carrier, cell, etc.). Each of the componentcarriers may be adjacent to each other or non-adjacent to each other.The bandwidth of each of the component carriers can be determinedindependently. An asymmetric carrier aggregation, which means that thenumber of downlink component carrier (DL CC) and the number of uplinkcomponent carrier (UL CC) are different from each other, is alsopossible. Meanwhile, control information can be set to be transceived ona specific CC only. The specific CC is called a primary CC and the restof CCs may be called a secondary CC.

If cross-carrier scheduling (or, cross-CC scheduling) is applied, PDCCHfor DL allocation is transmitted via a DL CC #0 and corresponding PDSCHcan be transmitted via a DL CC #2. For the cross-CC scheduling, it mayconsider introducing a CIF (carrier indicator field). A configurationinforming whether a CIF exists or not within a PDCCH can besemi-statically and user-specifically (or user group-specifically)enabled via an upper layer signaling (e.g., RRC signaling).

In case that a CIF exists within a PDCCH, a base station may be able toassign a monitoring DL CC set to reduce BD complexity of a userequipment side. The PDCCH monitoring DL CC set corresponds to a part ofthe entire aggregated DL CCs and includes one or more DL CCs. A userequipment may be able to perform a detection/decoding of the PDCCH on acorresponding DL CC only. In particular, the base station may be able totransmit the PDCCH via the monitoring DL CC set only. The PDCCHmonitoring DL CC set may be configured UE-specifically, UEgroup-specifically or cell-specifically. Such a term as PDCCH monitoringDL CC can be replaced with such an equivalent term as a monitoringcarrier, a monitoring cell, and the like. And, CCs aggregated for a UEcan be replaced with such an equivalent term as a serving CC, a servingcarrier, a serving cell, and the like.

FIG. 10 is a diagram for an example of a case that 3 DL CCs areaggregated and a DL CC A is configured as a monitoring DL CC. DL CCs Ato C can be referred to as a serving CC, a serving carrier, a servingcell, or the like. If a CIF is disabled, each of DL CCs may be able totransmit PDCCH, which schedules PDSCH of each of the DL CCs, without aCIF according to an LTE PDCCH rule. On the other hand, if the CIF isenabled by UE-specific (UE group-specific or cell-specific) upper layersignaling, only the DL CC A (monitoring DL CC) may be able to transmitthe PDCCH, which schedules the PDSCH of a different DL CC as well as thePDSCH of the DL CC A using the CIF. In this case, PDCCH is nottransmitted on a DL CC B and a DL CC C, which are not configured as aPDCCH monitoring DL CC. Hence, the DL CC A (monitoring DL CC) shouldinclude a PDCCH search space related to the DL CC A, a PDCCH searchspace related to the DL CC B, and a PDCCH search space related to the DLCC C. In the present specification, assume that a PDCCH search space isdefined according to a carrier.

As mentioned in the foregoing description, LTE-A considers using a CIFin PDCCH to perform cross-CC scheduling. Whether or not a CIF is used(i.e., whether or not cross-CC scheduling mode or non-cross-CCscheduling mode is supported) and switching between modes can besemi-statically or UE-specifically configured via RRC signaling. Afterthe RRC signaling is performed, a UE is able to recognize whether or nota CIF is used within PDCCH to be scheduled to the UE.

In the following, a HARQ (hybrid automatic repeat and request) in awireless communication system is explained.

When there exist a plurality of UEs having data to be transmitted inUL/DL in a wireless communication system, a base station selects a UE totransmit the data from among a plurality of the UEs at everytransmission unit time (transmission time interval (TTI) (e.g.,subframe)). In particular, in a system using multiple carriers or asystem similar to the system, the base station selects not only UEs totransmit data in UL/DL at every TTI but also a frequency band to be usedby each of the selected UEs to transmit the data.

On the basis of UL, if the UEs transmit a reference signal (or pilotsignal) to the base station in UL, the base station identifies channelstates of the UEs using the reference signal received from the UEs andselects UEs to transmit data in UL on each unit frequency band at everyTTI. The base station informs the UEs of a result of the selection. Inparticular, the base station transmits a UL assignment message to a UEUL scheduled at specific TTI to indicate the UE to transmit data using aspecific frequency band. The UL assignment message is also referred toas a UL grant. The UE transmits the data in UL according to the ULassignment message. Basically, the UL assignment message includesinformation on a UE ID (UE identity), RB allocation information,payload, etc. In addition, the UL assignment message can include an IR(incremental redundancy) version, NDI (new data indication), and thelike.

In case of using a synchronous non-adaptive HARQ scheme, when a UEscheduled at specific time performs retransmission, retransmission timeis systematically promised between the UE and the base station (e.g.,after 4 subframes from the timing at which NACK is received). Hence, thebase station can transmit the UL grant message to the UE at the initialtransmission only and the retransmission can be performed by ACK/NACKsignal. On the contrary, in case of using an asynchronous adaptive HARQscheme, since retransmission time is not promised between the basestation and the UE, it is necessary for the base station to transmit aretransmission request message to the UE. Moreover, since a frequencyresource for retransmission or MCS varies depending on transmissiontiming, the base station should transmit not only a UE ID, RB allocationinformation, and payload but also a HARQ process index, IR version, andNDI information to the UE at the time of transmitting the retransmissionrequest message to the UE.

FIG. 11 illustrates a UL HARQ operation in LTE system. In LTE system, aUL HARQ scheme uses synchronous non-adaptive HARQ. In case of using8-channel HARQ, HARQ process numbers are given by 0 to 7. One HARQprocess operates at every TTI (e.g., subframe). Referring to FIG. 11, abase station 810 transmits a UL grant to a UE 820 through PDCCH [S800].The UE transmits UL data to the base station 810 using an RB designatedby the UL grant and MCS after 4 subframes (e.g., subframe #4) from thetiming (e.g., subframe #0) at which the UL grant is received [S802].After the UL data received from the UE 820 is decoded, the base station810 generates ACK/NACK. If the base station fails to decode the UL data,the base station 810 transmits NACK to the UE 820 [S804]. The UE 820retransmits UL data to the base station after 4 subframes from thetiming at which the NACK is received [S806]. In this case, the initialtransmission and the retransmission of the UL data are performed by thesame HARQ process (e.g., HARQ process 4).

In the following, DL/UL HARQ operation in FDD system is explained.

FIG. 12 is a diagram for explaining a FDD system and a DL/UL HARQtimeline. In case of the FDD system illustrated in FIG. 12(a),transmission/reception of a DL/UL data corresponding to a specific UL/DLdata is received after 4 ms. Referring to FIG. 12(b), for example, ULACK/NACK is transmitted after 4 ms from the timing at which PDSCH/DLgrant is received in response to the PDSCH, PUSCH is transmitted after 4ms from the timing at which UL grant/PHICH is received in response tothe UL grant/PHICH, and PHICH/UL grant is received after 4 ms from thetiming at which PUSCH is transmitted/retransmitted in response to thePUSCH transmission/retransmission.

And, a synchronous HARQ scheme is used for a UL HARQ operation and anasynchronous HARQ scheme is used for a DL HARQ operation in 3GPP LTEsystem. The synchronous HARQ scheme corresponds to a scheme thatretransmission is performed at a timing determined by a system wheninitial transmission fails. In particular, transmission/retransmissionof UL data interlocked with a specific HARQ process or timing associatedwith a UL grant/PHICH timeline is defined in advance and it is difficultto randomly change the transmission/retransmission or the timing. On thecontrary, according to the asynchronous HARQ scheme, when an initialtransmission of data fails, retransmission of the data can be performedat a random timing appearing after 8 ms including the initialtransmission timing.

In the aforementioned FIGS. 11 and 12, each of the HARQ processes isdefined by a unique HARQ process identifier having a size of 3 bits andit is necessary for a receiving end (i.e., a UE in a DL HARQ process, aneNB in a UL HARQ process) to allocate an individual soft buffer tocombine retransmitted data.

In the following, HARQ timing in environment in which a TDD cell and aFDD cell are aggregated is explained. For example, assume that a TDDPcell and a FD Scell are aggregated by CA (carrier aggregation). If a UEapply DL timing (e.g., 4 ms) defined for legacy FDD to PDSCH receivedvia the FDD Scell as it is, since the TDD Pcell is configured by a DLsubframe at the DL HARQ timing, it may be difficult to transmitACK/NACK. Hence, when the TDD cell and the FDD cell are aggregated, itmay define new DL HARQ timing and new UL HARQ timing. Examples of thenew DL HARQ timing and the new UL HARQ timing are described in thefollowing.

DL HARQ timing for TDD Scell, in case of FDD Pcell

In case of performing self-scheduling and cross carrier scheduling, HARQtiming for PDSCH of the TDD Scell can be configured to be identical toHARQ timing for the FDD Pcell. For example, ACK/NACK information onPDSCH of the Scell can be transmitted via the Pcell.

UL HARQ timing for TDD Scell, in case of FDD Pcell

Self-scheduling: HARQ timing for PUSCH transmitted via the Scell can beconfigured based on HARQ timing scheduled to the TDD cell.

Cross carrier scheduling: (i) Similar to the self-scheduling, HARQtiming for PUSCH transmitted via the Scell can be configured based onHARQ timing scheduled to the TDD cell. (ii) Or, ACK/NACK information canbe received via PHICH after 6 ms from timing at which PUSCH istransmitted via the Scell. (iii) Or, HARQ timing can be configured basedon reference UL-DL configuration obtained by a scheduling cell.

DL HARQ timing for FDD Scell, in case of TDD Pcell

Self-scheduling: (i) HARQ timing for PDSCH of the Scell can beconfigured by additional timing different from HARQ timing of the TDDPcell and HARQ timing of the TDD Pcell based on UL-DL configuration ofthe TDD Pcell. Or, It may define new timing including more DL subframesthan the legacy TDD Pcell HARQ timing according to UL-DL configurationof the TDD Pcell. For details, it may refer to Table 5 in the following.(ii) Or, HARQ timing for PDSCH of the Scell can be determined based onreference UL-DL configuration set to the FDD Scell. The reference UL-DLconfiguration can be determined based on UL-DL configuration of the TDDPcell. And, it may configure additional HARQ timings different from theHARQ timing of the TDD Pcell. For more details, it may refer to Tables6, 7, and 8 in the following.

Cross carrier scheduling: HARQ timing for PDSCH of the Scell can beconfigured to be identical to the self-scheduling or the HARQ timing ofthe TDD Pcell.

UL HARQ timing for FDD Scell, in case of TDD Pcell

Self scheduling: HARQ timing for PUSCH transmitted via the Scell can beconfigured by FDD HARQ timing.

Cross carrier scheduling: (i) HARQ timing for PUSCH transmitted via theScell may follow HARQ timing of the TDD Pcell or FDD HARQ timing. (ii)Or, as an example, ACK/NACK information can be received via PHICH after6 ms from timing at which PUSCH is transmitted via the Scell. Unlikely,it may configure by FDD HARQ timing.

Table 5 corresponds to a TDD Pcell case and shows detail examples of (i)the self-scheduling case of the DL HARQ timing (e.g., ‘DL associationset index’) for the FDD Scell.

TABLE 5 UL-DL HARQ Subframe n Conf. timing 0 1 2 3 4 5 6 7 8 9 0 0A — —6, [5] [5], [4] 4 — — 6, [5] [5], [4] 4 0 0B 6, [5], [4] [5], 4 6, [5],[4] [5], 4 1 1 — — 7, 6, [5] [5], 4 — — — 7, 6, [5] [5], 4 — 1 1* 7, 6[6], [5], 4 7, 6 [6], [5], 4 2 2 — — 8, 7, 6, [5], 4 — — — — 8, 7, 6,[5], — — 4 3 3 — — 11, [10], [9], [8], 7, 6, 5 5, 4 — — — — — 6 3 3a — —11, [10], 7, 6 [10], 6, 5 [10], 5, 4 4 4 — — 12, 11, [10], [9], 8, 7, 6,5, 4 7 4 4a 12, 11, [10], 8, 7 [10], 7, 6, 5, 4 5 5 — — 13, 12, 11,[10], 9, — — — — — — — 8, 7, 6, 5, 4 6 6 — — [8], 7 7, [6] [6], 5 — — 77, [6], [5] — 6 6* — — 7 7, [6], [5] 5 — — 7, [6], [5], 7 — [4]

In Table 5, UL-DL configuration may correspond to U/D configuration ofthe TDD Pcell. DL HARQ timing for the FDD Scell can be defined by atype/index of HARQ timing associated with the TDD Pcell U/D. ‘DLassociation set index’ may correspond to “[]” in Table 5. In particular,the “[]” may correspond to a DL association set index added to the TDDPcell U/D configuration. For example, in case of UL-DL configuration 0and HARQ timing 0A, a subframe #2 transmit ACK/NACK for PDSCH (i.e.,subframe #6 of a previous frame) of the FDD Scell which is received 5subframes ahead and ACK/NACK for PDSCH (i.e., subframe #7 of a previousframe) of the FDD Scell which is received 6 subframes ahead,respectively. A subframe #3 transmit ACK/NACK for PDSCH (i.e., subframe#8 of a previous frame) of the FDD Scell which is received 5 subframesahead and ACK/NACK for PDSCH (i.e., subframe #9 of a previous frame) ofthe FDD Scell which is received 4 subframes ahead, respectively.

Tables 6, 7, and 8 correspond to a TDD Pcell case and shows detailexamples of (ii) the self-scheduling case of the DL HARQ timing (e.g.,‘DL association set index’) for the FDD Scell.

TABLE 6 TDD PCell Allowed reference U/D configuration configuration forFDD SCell 0 {0, 1, 2, 3, 4, 5, 6} 1 {1, 2, 4, 5} 2 {2, 5} 3 {3, 4, 5} 4{4, 5} 5 {5} 6 {1, 2, 3, 4, 5, 6}

TABLE 7 TDD PCell Allowed reference U/D configuration configuration forFDD SCell 0 {2, 4, 5} 1 {2, 4, 5} 2 {2, 5} 3 {4, 5} 4 {4, 5} 5 {5} 6 {2,4, 5}

TABLE 8 Allowed reference Allowed reference configuration configurationfor FDD SCell TDD PCell for FDD SCell (more than 2 U/D configuration (2aggregated cells) aggregated cells) 0 5 2 1 5 2 2 5 2 3 5 4 4 5 4 5 5Not applicable 6 5 2

In the following, ACK/NACK multiplexing or bundling scheme is explained.

An ACK/NACK multiplexing (i.e., ACK/NACK selection) method applied toRel-8 TDD system considers an ACK/NACK selection scheme that uses animplicit PUCCH resource corresponding (i.e., linked to a lowest CCEindex) to PDCCH scheduling each PDSCH of a UE to secure a PUCCH resourceof the UE.

Meanwhile, LTE-A FDD system basically considers transmitting a pluralityof ACKs/NACKs in response to a plurality of PDSCHs, which aretransmitted via a plurality of DL component carriers, through aUE-specifically configured specific UL CC. To this end, LTE-A FDD systemconsiders “ACK/NACK selection” scheme using an implicit PUCCH resourcelinked with PDCCH that schedules a specific DL component carrier, a partof DL component carriers, or all DL component carriers (i.e., linkedwith a lowest CCE index nCCE, or nCCE and nCCE+1), or a combination ofthe implicit PUCCH resource and an explicit PUCCH resource reserved toeach UE in advance via RRC signaling.

LTE-A TDD system can also consider a situation that pluralities ofcomponent carriers are aggregated. Hence, it may consider transmitting aplurality of ACK/NACK information/signals in response to a plurality ofPDSCHs, which are transmitted via a plurality of DL subframes and aplurality of component carriers, in UL subframes corresponding to aplurality of the DL subframes via a specific CC (i.e., AN/CC). In thiscase, unlike the LTE-A FDD, it may consider a scheme of transmitting aplurality of ACKs/NACKs corresponding to the maximum number of CWscapable of being transmitted via all component carriers assigned to a UEto all of a plurality of DL subframes (i.e., full ACK/NACK) or a schemeof transmitting ACKs/NACKs by reducing the number of ACKS/NACKs byapplying ACK/NACK bundling to CW and/or CC and/or SF domain (i.e.,bundles ACK/NACK). In this case, in case of the CW bundling, ACK/NACKbundling for CW is applied to each DL subframe according to a componentcarrier. In case of the CC bundling, ACK/NACK bundling for all or a partof CCs is applied to each DL subframe. In case of the SF bundling,ACK/NACK bundling for all or a part of DL SFs is applied to each CC.

Meanwhile, LTE-A system considers transmitting a plurality of ACK/NACKinformation/signals for a plurality of PDSCHs, which are transmitted viaa plurality of DL component carriers (DL CCs), via a specific ULcomponent carrier (UL CC). In this case, unlike ACK/NACK transmissionusing a PUCCH format 1a/2b in legacy Rel-8 LTE, it may consider a methodof transmitting a plurality of ACK/NACK information and/or controlsignals using a PUCCH format 2 or a PUCCH format 3 corresponding to aform modified based on block-spreading scheme after channel coding(e.g., Reed-Muller code, Tail-biting convolutional code, etc.) isperformed on a plurality of the ACK/NACK information.

In this case, the block-spread scheme corresponds to a method ofmodulating control information (e.g., ACK/NACK, etc.) transmission usingSC-FDMA scheme rather than a PUCCH format 1 or 2 of legacy LTE.According to the block-spread scheme, a symbol sequence can betransmitted in a manner of being spread in time domain by an OCC(orthogonal cover code). In this case, it may be able to multiplexcontrol signals of a plurality of UEs with the same resource block (RB)using the OCC.

5 GHz unlicensed band or 2.4 GHz unlicensed band used by WiFi system canbe utilized for traffic offloading.

FIG. 13 is a diagram for an example of a method of using an unlicensedband.

For clarity, assume a situation that a communication node is configuredto perform wireless communication via a CC of a licensed band and a CCof an unlicensed band. According to the embodiment of FIG. 13, an eNBmay transmit a signal to a UE or the UE may transmit a signal to the eNBin a CA (carrier aggregation) situation of the LTE/LTE-A licensed bandand the LTE-U unlicensed band.

ACC of a licensed band can be referred to as L-CC (licensed CC) orL-cell (licensed CC) as well. A CC of an unlicensed band can be referredto as U-CC (unlicensed band CC) or U-cell (unlicensed band CC) as well.For clarity, it may assume that a CC accessed by a UE in the U-band isU-Scell and a CC accessed in the L-band is Pcell. For clarity, assumethat a Pcell (PCC) is positioned at a licensed band and at least one ofSCells (SCC) is positioned at an unlicensed band, by which the presentinvention may be non-limited. For example, a plurality of licensed bandsand a plurality of unlicensed bands can be CA or a signal can betransceived between the eNB and the UE on an unlicensed band only.

DL transmission of an eNB or UL transmission of a UE is not alwaysguaranteed in U-band. Hence, an LTE UE operating on the U-band mayaccess a different cell operating on L-band (licensed band) to stablycontrol mobility, an RRM (radio resource management) function, and thelike. Moreover, the embodiments of the present invention can beextensively applied not only to 3GPP LTE/LTE-A system, but also to otherwireless communication systems.

A scheme of performing data transmission and reception on U-band using acombination with L-band is commonly referred to as LAA (licensedassisted access). If U-cell positioned at U-band is used by the LAAscheme, the U-cell can be simply referred to as LAA-cell. For example,LAA-Scell may correspond to a Scell positioned at an unlicensed bandused by the LAA scheme. For clarity, such a term as LAA-(S)cell, U-band,and U-(S)cell can be used in a manner of being mixed. And, a cell canalso be referred to as a CC (component carrier) or a carrier.

Since an unlicensed band basically assumes that wireless transmissionand reception are performed via contention between communication nodes,it is required for each communication node to perform channel sensing(CS) before a signal is transmitted to check whether or not a differentcommunication node transmits a signal. The channel sensing is referredto as CCA (clear channel assessment) or carrier sensing. An eNB or a UEof LTE system can also perform the CCA to transmit a signal in anunlicensed band.

As an example of an unlicensed band operation operating with acontention-based random access scheme, a communication node (e.g., eNB)checks whether a current channel of an UCell is busy or idle byperforming carrier sensing (CS) before a data is transmitted andreceived. For example, when there is a CCA (Clear Channel Assessment)threshold configured by predefined signaling or a higher layersignaling, if energy higher than the CCA threshold is detected in theUCell, it is determined as the UCell is in a busy state. Otherwise, itis determined as the UCell is in an idle state. If it is determined asthe UCell is in the idle state, the communication node can start signaltransmission in the UCell. This kind of procedure is referred to aslisten-before-talk (LBT).

For example, when an eNB or a UE transmits a signal in the LTE system,it is necessary for other communication nodes such as WiFi and the liketo perform the LBT not to cause any interference. For example, a CCAthreshold is regulated by −62 dBm for a non-WiFi signal and −82 dBm fora WiFi signal, respectively, in WiFi standard (e.g., 802.11ac). Forexample, if a non-WiFi signal is received with power equal to or greaterthan −62 dBm, an STA or an AP does not transmit a signal in order not tocause any interference. When the STA or the AP performs CCA in WiFisystem, if a signal equal to or greater than the CCA threshold is notdetected for more than 4 us, the STA or the AP can perform signaltransmission.

For example, regulation of Europe illustrates two types of LBT-basedoperation respectively referred to as FBE (frame based equipment) andLBE (load based equipment).

FIG. 14 illustrates a FBE operation according to ETSI regulation (EN 301893 V1.7.1) and FIG. 15 illustrates a flow of the FBE operation.

Referring to FIGS. 14 and 15, the FBE configures a single fixed frameusing channel occupancy time (e.g., 1-10 ms) corresponding to timecapable of maintaining transmission when a communication node succeedsin accessing a channel and an idle period corresponding to the minimum5% of the channel occupancy time. In this case, CCA is performed via aCCA slot (e.g., minimum 20 us) defined at an end part of the idleperiod. The communication node periodically performs the CCA in a unitof the fixed frame. If a channel is unoccupied, the communication nodetransmits data during the channel occupancy time. If a channel isoccupied, the communication node waits until a CCA slot of a next periodwhile postponing transmission.

FIG. 16 illustrates an LBE operation and FIG. 17 illustrates a flow ofthe LBE operation.

Referring to FIGS. 16 and 17, in case of the LBE, a communication nodeconfigures a value of q∈ {4, 5, . . . , 32} first and performs CCA on asingle CCA slot. If a channel is unoccupied in the first CCA slot, thecommunication node can transmit data by securing channel occupancy timeas much as a length of (13/32)q ms. If a channel is occupied in thefirst CCA slot, the communication node randomly selects a value of N∈{1, 2, . . . , q}, stores the selected value as an initial value of acounter, and senses a channel state in a unit of a CCA slot. If achannel is unoccupied in a specific CCA slot, the communication nodereduces the value stored in the counter by 1. If the value of thecounter becomes 0, the communication node can transmit data by securingtime as much as a length of (13/32)q ms.

CCA in U-Cell Operating Based on LAA

Recently, 3GPP LTE system is considering a method of managing aplurality of U-Scells in U-band as a technology for LAA. According tothe ETSI regulation, when transmission power of entire signalstransmitted on U-band is fixed, if a bandwidth on which the signals aretransmitted increases (i.e., if the number of U-scells increases), a CCAthreshold can be reduced. For example, according to the ETSI regulation,if PH corresponding to specific transmit power is equal to or less than23 dBm, a CCA threshold (TL) can be calculated as equation 1 describedin the following.

TL=−73 dBm/MHz+(23 dBm−P _(H))/(1 MHz)   [Equation 1]

Referring to equation 1, the TL is defined on the basis of 1 MHz unitchannel size. In particular, the CCA threshold is defined in proportionto a size of a bandwidth to be actually transmitted by a transmitter.

For example, when transmit power corresponds to 23 dBm and a transmittertransmits a bandwidth of a size of 20 MHz (e.g., 1 U-Scell), the TLbecomes −73 dBm/MHz*20 MHz=−60 dBm. In this case, ‘*20 MHz’ means that aCCA threshold power value for 1 MHz channel increases 20 times.Specifically, since −73 dBm corresponds to 10^(−7.3) mW, the meaning of−73 dBm/MHz*20 MHz corresponds to 10^(−7.3)×20 mW. If the 10^(−7.3)×20mW is converted into a dBm unit, it may obtain 10×log 10(10^(−7.3)×20)=−60 dBm. In this case, the ‘log 10 ( )’ corresponds to acommon log having a base as much as 10.

As a different example, when transmit power corresponds to 23 dBm and atransmitter transmits a bandwidth of a size of 40 MHz (e.g., 2U-Scells), the TL becomes −73 dBm/MHz*40 MHz=−57 dBm. As a furtherdifferent example, when transmit power corresponds to 20 dBm and atransmitter transmits a bandwidth of a size of 20 MHz (e.g., 1 U-Scell),the TL becomes −70 dBm/MHz*20 MHz=−57 dBm. When transmit powercorresponds to 20 dBm and a transmitter transmits a bandwidth of a sizeof 40 MHz (e.g., 2 U-Scells), the TL becomes −70 dBm/MHz*40 MHz=−54 dBm.In particular, the CCA threshold may change according to transmit powerand a bandwidth of a signal transmitted on U-band.

Adjustment of Transmit Power

When a plurality of nodes perform signal transmission based on LBT(listen before talk) in a wireless communication system and a CCA(channel assessment) threshold changes according to transmit power of atransmission node and a transmission bandwidth, methods of adjusting thetransmit power are proposed according to the number of U-Scells capableof transmitting a signal according to an LBT operation on a U-band(unlicensed band).

Proposal #1

Assume a situation that a transmission node configures a transmit powervalue by P₀ for U-band and intends to transmit a signal to the N₁ numberof U-Scells. When the transmission node succeeds in performing channelaccess on the N₂ (<N₁) number of U-SCells by performing LBT using a CCAthreshold TL₀ corresponding to the P₀ and the entire bandwidth (BW₁) ofthe N₁ number of U-SCells, it may be able to adjust transmit poweraccording to one of methods described in the following.

(1) When a P_(x) is selected under the condition that an LBT result isnot changed by a CCA threshold TL_(x) corresponding to transmit powerP_(x) and the entire bandwidth BW₂ of the N₂ number of U-SCells, amaximum value of the P_(x) is configured as transmit power fortransmitting the entire signals on U-band.

(2) When transmit power P₁=P₀*(BW₂/BW₁) and a CCA threshold TL₁corresponding to BW₂ do not change an LBT result, the P₁ is configuredas transmit power for transmitting the entire signals on U-band.

For example, when both LTE system according to the embodiment of thepresent invention and ETSI regulation are applied at the same time,assume that an eNB has transmit power of 23 dBm. In this case, the eNBmay prepare to transmit PDSCH to two U-SCells (e.g., U-Scell₁ andU-Scell₂) each of which has 20 MHz bandwidth using 20 dBm (i.e., 20dBm+20 dBm=23 dBm). In order to transmit the PDSCH, the eNB performs LBTusing 23 dBm and −57 dBm CCA threshold corresponding to 40 MHz (i.e.,20+20 MHz). When LBT is performed at specific timing, if it isdetermined that signal transmission is available in a single U-Scellonly, the eNB can simply assign the entire transmit power of 23 dBm tothe single U-Scell (e.g., U-SCell₂) capable of performing signaltransmission.

However, the abovementioned case corresponds to a case that a BW ischanged while transmit power is fixed. Hence, according to the ETSIregulation, the eNB should perform the LBT on the basis of a value(i.e., −60 dBm) that the CCA threshold is reduced as much as 3 dB.Depending on channel environment, the CCA threshold of −60 dBm maychange a legacy LBT result (e.g., U-Scell₂ is idle) of which the CCAthreshold is not changed. In other word, it may determine that a signalis not transmitted in the U-Scell₂ (e.g., U-Scell₂ is busy).

In particular, the eNB can apply a maximum transmit power value within arange capable of identically maintaining the legacy LBT result.

Or, in order to avoid a dynamic change of transmit power, the eNB mayapply transmit power corresponding to the number of U-SCells (or, theentire bandwidth of U-SCells) selected according to an LBT operation.For example, as mentioned in the foregoing description, when an LBToperation is performed on 2 U-SCells, if it is determined that a singleU-Scell is available only, it may configure 20 dBm corresponding to thehalf of the initially intended transmit power (i.e., 23 dBm) as transmitpower in U-band. In this case, since a CCA threshold is applied by avalue higher than the transmit power as much as 3 dB, the legacy LBTresult can be identically maintained.

Proposal #2

According to one embodiment, a transmission node (or, an eNB) transmitsinformation on U-SCells (i.e., number of U-Cells and a transmit powervalue in each U-Scell), which are assumed by the transmission node toconfigure transmit power, to a reception node (or, a UE) in advance.Having received the information, the reception UE may assume that thetransmit power is semi-statically changed.

For example, in case of the operation (2) of the proposal #1, an eNBcalculates maximum transmit power by assuming the number of U-SCells tobe managed by the eNB and may be able to calculate transmit power perU-Scell by dividing the maximum transmit power by the number of theU-SCells. The eNB may maintain the transmit power per U-Scellirrespective of an LBT operation.

In this case, the eNB can provide the U-Scell information, which isassumed to calculate the transmit power, to the UE to prevent the UEfrom assuming that the transmit power is dynamically changed.

Proposal #3

When a separate control node indicates a transmission node to transmit asignal with transmit power of P_(TX), if the P_(TX) is greater thanP_(CMAX) corresponding to a maximum transmit power limit of thetransmission node, the transmit power can be adjusted according to oneof methods described in the following.

(1) The transmission node determines whether to perform transmission byapplying a CCA threshold on the basis of the P_(TX) and a transmissionbandwidth. When the transmission node practically performs transmission,the transmission is performed by lowering transmit power using theP_(CMAX).

(2) The transmission node determines whether to perform transmission byapplying a CCA threshold using P_(CMAX) and performs transmission usingthe P_(CMAX).

For example, when UL transmission is performed, transmit power of a UEcan be configured according to an indication of an eNB. Yet, in somecases, the eNB may set a transmit power value (P_(TX)), which is greaterthan a P_(CMAX) value corresponding to the maximum transmit power valueof the UE, to the UE via power control. If the UE is able to configure aCCA threshold according to the P_(TX), the UE is able to comprehend theP_(TX) as a value signaled by the eNB to indicate the CCA threshold. Inparticular, the UE may follow the P_(CMAX) to practically transmit asignal while performing an LBT operation by calculating a CCA thresholdaccording to the P_(TX).

Or, the UE may determine the P_(TX) indication of the eNB as an errorand performs an LBT operation by calculating a CCA threshold accordingto the P_(CMAX). In this case, the P_(CMAX) can be applied as transmitpower for practically transmitting a signal.

Proposal #4

Assume that a separate control node indicates a transmission node totransmit a signal to a plurality of U-Scells (i.e., [U-SCell₁, U-SCell₂,. . . , U-SCell_(N)]) using transmit power per UScell (i.e., [P_(TX, 1),P_(TX, 2), . . . , P_(TX, N)]). If the sum (i.e., P_(TX, 1)+P_(TX, 2) .. . +P_(TX, N)=P_(TX)) of the transmit power per UScell has a valuegreater than a maximum transmit power limit (P_(CMAX)) of thetransmission node, transmit power can be adjusted using one of methodsdescribed in the following.

For clarity, assume that [P_(TX, 1)′, P_(TX, 2)′, . . . , P_(TX, N)′] isdefined as transmit power per U-Scell satisfying P_(TX, 1)′+P_(TX, 2)′+. . . +P_(TX, N)′=P_(CMAX). In this case, the P_(TX, i)′ is equal to orless than the P_(TX, i) and the i corresponds to 1, 2, . . . , N.

(1) The transmission node determines whether to perform transmission byapplying a CCA threshold on the basis of [P_(TX, 1), P_(TX, 2), . . . ,P_(TX, N)] (or, P_(TX)) and a transmission bandwidth for the N number ofU-SCells. In this case, the transmission node performs transmission byapplying transmit power per U-Scell selected from among [P_(TX, 1)′,P_(TX, 2)′, . . . , P_(TX, N)′] to U-Scell in which actual transmissionis performed.

(2) The transmission node determines whether to perform transmission byapplying a CCA threshold on the basis of [P_(TX, 1)′, P_(TX, 2)′, . . ., P_(TX, N)′] (or, P_(CMAX)) and a transmission bandwidth for the Nnumber of U-SCells. In this case, the transmission node performstransmission by applying transmit power per U-Scell selected from among[P_(TX, 1)′, P_(TX, 2)′, . . . , P_(TX, N)′] to U-Scells in which actualtransmission is performed.

(3) The transmission node determines whether to perform transmission byapplying a CCA threshold on the basis of [P_(TX, 1)′, P_(TX, 2)′, . . ., P_(TX, N)′] (or, P_(CMAX)) and a transmission bandwidth for the Nnumber of U-SCells. As mentioned earlier in the ‘proposal #1’, thetransmission node adjusts the total transmit power for U-Scells capableof performing actual transmission using P_(CMAX,LBT). The transmissionnode performs transmission by performing scaling on transmit power perU-Scell selected from among [P_(TX, 1)′, P_(TX, 2)′, . . . , P_(TX, N)′]using (P_(CMAX,LBT)/P_(CMAX)).

(4) The transmission node determines whether to perform transmission byapplying a CCA threshold on the basis of [P_(TX, 1), P_(TX, 2), . . . ,P_(TX, N)] (or, P_(TX)) and a transmission bandwidth for the N number ofU-SCells. The transmission node selects UScells capable of performingtransmission according to a priority under the condition that the sum ofthe transmit power of the U-SCells is equal to or less than P_(CMAX).The transmission node performs transmission by applying transmit powerper U-Scell selected from among [P_(TX, 1), P_(TX, 2), . . . ,P_(TX, N)].

(5) The transmission node selects UScells capable of performingtransmission according to a priority under the condition that the sum ofthe transmit power of the U-SCells is equal to or less than P_(CMAX).The transmission node determines whether or not each U-Scell performstransmission by applying a CCA threshold on the basis of the sum(P_(TX, S)) of transmit power (e.g., P_(TX, i), i=1, 2, . . . , N)indicated to the selected U-SCells by the eNB and a transmissionbandwidth for the selected U-Scells. The transmission node appliestransmit power per U-Scell selected from among [P_(TX, 1), P_(TX, 2), .. . , P_(TX, N)] to the U-SCells.

(6) If the transmission node corresponds to a UE, the UE selectsU-Scells to make the sum of transmit power of U-Scells to be equal to orless than P_(CMAX). When the UE selects the U-Scells, the UE can selectthe U-Scells according to a predetermined priority. The UE calculatesP_(TX, S) corresponding to the sum of transmit power (e.g., P_(TX, i),i=1, 2, . . . . , N) indicated by the eNB for the selected U-SCells. TheUE determines a CCA threshold on the basis of the P_(TX, S) and theentire transmission bandwidth of the selected U-SCells and determinesU-SCells capable of performing transmission using the determined CCAthreshold. Subsequently, as mentioned earlier in the proposal #1, the UEadjusts transmit power for the entire U-band using P_(TX, S, LBT) basedon the U-Scells capable of performing transmission according to an LBToperation. The UE can perform scaling on transmit power of the U-SCellsselected from among [P_(TX, 1), P_(TX, 2), . . . , P_(TX, N)] using(P_(TX, S, LBT)/P_(TX, S)).

For example, when UL transmission is performed, assume a state that theUE sets UL power control to make a PUSCH to be transmitted on a CC1 anda CC2 defined in U-band using P_(TX1) and P_(TX2), respectively. If amaximum transmit power limit of the UE is set to the entire U-band usingP_(CMAX) (in this case, P_(TX1)+P_(TX2)>P_(CMAX)), it may consideroperations described in the following.

(a) The UE performs LBT by applying a CCA threshold on the basis of theP_(TX1) and the P_(TX2). In case of transmitting both, each of transmitpowers can be lowered to P_(TX1)′ and P_(TX2)′, respectively. (In thiscase, P_(TX1)′+P_(TX2)′=P_(CMAX))

(b) If the UE performs LBT by applying a CCA threshold on the basis ofP_(TX1)′ and P_(TX2)′, the UE is able to transmit both CCs. Yet, if theUE performs LBT by applying a CCA threshold on the basis of P_(TX1) andP_(TX2), it may fail to transmit a CC. In this case, (i) the UEtransmits both CCs by configuring transmit power using P_(TX1)′ andP_(TX2)′ or (ii) the UE may transmit one CC only using transmit power ofP_(TX1) or P_(TX2).

In particular, if a UL power control value indicated by the eNB exceedsa maximum transmit power value of the UE, the UE can recognize the ULpower control value indicated by the eNB as a value indicated for theusage of a CCA threshold. Or, the UE may recognize the UL power controlvalue indicated by the eNB as an improperly indicated value andconfigures a CCA threshold based on a maximum transmit power value ofthe UE to perform an LBT operation. Or, the UE may recognize the ULpower control value indicated by the eNB as transmit power intended bythe eNB and may be able to perform an LBT operation using a CCAthreshold according to the indicated transmit power value. As a resultof the LBT operation, the UE can perform signal transmission on maximumU-Scells capable of performing transmission only.

Proposal #5

When a maximum transmit power limit P_(CMAX) of a transmission node isset and a correlation among transmit power, a transmission bandwidth,and a CCA threshold exists, it may adjust the transmit power and the CCAthreshold without following the correlation in the following cases.

(1) The CCA threshold is increased when the transmit power is decreased.If a maximum CCA threshold is set, a transmission node may configure theincreased CCA threshold to be equal to or less than the maximum CCAthreshold while decreasing the transmit power.

(2) The CCA threshold is decreased when the transmit power is increased.If a minimum CCA threshold is set, (i) a transmission node may set alimit on a maximum value of transmit power using a transmit power valuecorresponding to the minimum CCA threshold or, (ii) the transmissionnode may set a limit on the maximum value of the transmit power usingP_(CMAX).

For example, referring to equation 1, if transmit power is reduced to 18dBm, a CCA threshold increases. In this case, if a signal is transmittedon 20 MHz band, the CCA threshold can be configured by (−73+5)dBm/MHz*20 MHz=−55 dBm.

Yet, if WiFi devices currently existing on U-band transmit a signal on20 MHz band, the CCA threshold may have a value up to maximum −62 dBm.In order for lately introduced LAA cells to coexist with Wi-Fi, amaximum CCA threshold identical to that of the WiFi can also be set tothe LAA cells. Hence, although transmit power is decreased, the CCAthreshold may not be increased more than a specific value. Or, as a caseof increasing transmit power, if a minimum CCA threshold is set, amaximum value of transmit power can be limited by transmit powercorresponding to the minimum CCA threshold. For example, in equation 1,a minimum CCA threshold corresponds to −73 dBm and transmit powercorresponding to the minimum CCA threshold corresponds to 23 dBm. Hence,it may set a limit on maximum transmit power to make the maximumtransmit power to be equal to or less than 23 dBm.

Proposal #6

When transmit power of a transmission node varies according to an LBToperation in a plurality of U-SCells, a range for a ratio of CRS EPRE(energy per resource element) to PDSCH EPRE (or, a parameter determiningthe ratio) can be changed according to a carrier type (or, higher layersignal or DCI).

In a wireless communication system such as 3GPP LTE, and the like, EPRE(energy per resource element) is defined for power allocation of adownlink resource. In this case, CRS EPRE may become a reference. TheCRS EPRE is configured by a higher layer signal. The CRS EPRE has afixed value in a downlink system band and a subframe. A PDSCH EPRE canbe represented by a certain ratio of the CRS EPRE. For example, a ratioof the CRS EPRE to the PDSCH EPRE is defined by ρ_(A) in an OFDM symbolwhere a CRS does not exist. The ratio of the CRS EPRE to the PDSCH EPREis defined by ρ_(B) in an OFDM symbol where a CRS exists. In this case,the ρ_(A) is determined by a power offset δ_(power-offset) according towhether or not MIMO is applied and P_(A) corresponding to a UE-specificvariable. ρ_(B)/ρ_(A) is determined by the number of antenna ports andP_(B) corresponding to a cell-specific variable.

In LTE system (e.g., Rel-12), the ρ_(A) is differently defined for twocases. When PDSCH data is transmitted based on a transmission diversityscheme via 4 cell-common antenna ports, the ρ_(A) is determined byequation 2.

ρ_(A)=δ_(power-offset) +P _(A)10 log₁₀(2)_([dB])  [Equation 2]

In this case, δ_(power-offset) corresponds to a power offset value forsupporting a MU-MIMO operation and the δ_(power-offset) is set to 0 dBwhen other PDSCH is transmitted. P_(A) corresponds to a UE-specificvariable. For example, referring to Table 9, a parameter ‘p-a’corresponds to the P_(A) and the P_(A) may have a value selected fromamong [−6 dB, −4.77 dB, −3 dB, −1.77 dB, 0 dB, 1 dB, 2 dB, 3 dB].

TABLE 9 PDSCH-Config information element -- ASN1START PDSCH-ConfigCommon::= SEQUENCE { referenceSignalPower INTEGER (−60..50), p-b INTEGER(0..3)} PDSCH-ConfigDedicated::= SEQUENCE { p-a ENUMERATED { dB-6,dB-4dot77, dB-3, dB-1dot77, dB0, dB1, dB2, dB3}} -- ASN1STOP

The P_(A) is defined by equation 3 except a case of transmitting PDSCHbased on transmission diversity.

ρ_(A)=δ_(power-offset) +P _(A [dB])  [Equation 3]

In LTE system, a cell-specifically defined P_(B) corresponds to a ratioof ρ_(B)/ρ_(A) according to the number of antenna ports. Referring toTable 9, a parameter ‘p-b’ corresponds to the P_(B) and has a valueselected from among 0 to 3. And, Table 10 illustrates transmit powerallocation according to each P_(B) value ranging from 0 to 3.

TABLE 10 ρ_(B)/ρ_(A) One Two and Four P_(B) Antenna Port Antenna Ports 01 5/4 1 4/5 1 2 3/5 3/4 3 2/5 1/2

In this case, as mentioned in the foregoing description, in U-band,transmit power may vary according to the number of U-SCells capable ofpractically performing transmission according to an LBT operation.Hence, a difference between the CRC EPRE and the PDSCH EPRE can beincreased compared to a legacy LTE system.

Hence, one embodiment of the present invention proposes a method ofchanging a range of a ratio of the CRS EPRE to the PDSCH EPRE accordingto a carrier type (or, higher layer signal or DCI). For example, it maymore expand a range of the P_(A) in U-band. Specifically, the range ofthe P_(A) can be expanded to [−9 dB, −7.77 dB, −6 dB, −4.77 dB, −3 dB,−1.77 dB, 0 dB, 1 dB, 2 dB, 3 dB].

The P_(B) can also be expanded as shown in Table 11.

TABLE 11 ρ_(B)/ρ_(A) One Two and Four P_(B) Antenna Port Antenna Ports 01 5/4 1 4/5 1 2 3/5 3/4 3 2/5 1/2 4 1/5 1/4

The aforementioned proposal #6 can also be applied to an arbitrary RS.In particular, a ratio of specific RS power to PDSCH power can beconfigured to have a different range according to a carrier type (or,higher layer signal or DCI) and an eNB can inform a UE of theinformation. For example, when it is able to indicate a ratio of CSI-REEPRE to PDSCH EPRE in a unit of 1 dB in L-band (e.g., P_(C) is theassumed ratio of PDSCH EPRE to CSI-RS EPRE when UE derives CSI feedbackand takes values in the range of [−8, 15] dB with 1 dB step size), arange can be expanded to [−10, 20] dB and the like in U-band.

Proposal #7

An eNB sets (reference) CRS EPRE for transmitting a discovery signal toa UE in U-band and can signal a CRS EPRE value for transmitting PDSCHusing a ratio value compared to the (reference) CRS EPRE. In this case,the (reference) CRS EPRE (1) can be applied in discovery signal occasion(i.e., a section in which a discovery signal is actually transmitted)only, or (2) can be applied in a DMTC (Discovery signals measurementtiming configuration) section (i.e., a section in which a discoverysignal is expected to be transmitted).

In particular, it is preferable to fix transmit power of a CRS, which istransmitted as a discovery signal for measuring RRM, even in a situationthat the transmit power is dynamically changed. In this case, CRS EPREfor transmitting a discovery signal may become a reference value forindicating power of different transmission signals. For example, a CRSEPRE value for transmitting PDSCH also corresponds to a ratio valuecompared to CRS EPRE (e.g., reference CRS EPRE) for transmitting adiscovery signal. The CRS EPRE value can be transmitted to a UE viahigher layer signaling (e.g., RRC signaling) or dynamic L1 signaling(e.g., DCI).

The proposal #1 can also be applied to an arbitrary RS. For example, aneNB can inform a UE of a ratio of specific RS power to reference CRSpower via higher layer signaling (e.g., RRC signaling) or dynamic L1signaling (e.g., DCI).

CCA Threshold

The aforementioned CCA threshold can also be referred to as an energydetection threshold.

First of all, when DL transmission defined in LTE Rel-13 system isperformed, an energy detection threshold for an LBT operation isexplained. An eNB accessing a channel on which LAA Scell transmission isperformed should configure an energy detection threshold (X_(Thresh)) tobe equal to or less than a maximum energy detection threshold(X_(Thresh) _(_) _(max)). In this case, the maximum energy detectionthreshold (X_(Thresh) _(_) _(max)) varies according to whether or not itis able to share a carrier on which LBT is performed by a differentwireless access technology (e.g., WiFi, etc.) on a long term basis.

If an absence of the different wireless access technology sharing thecarrier is guaranteed on a long term basis, the maximum energy detectionthreshold (X_(Thresh) _(_) _(max)) is defined as equation 4 described inthe following.

$\begin{matrix}{X_{Thresh\_ max} = {\min \begin{Bmatrix}{{T_{\max} + {10\mspace{14mu} {dB}}},} \\X_{r}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In equation 4, T_(max) corresponds to a value determined according to abandwidth of a corresponding carrier. The T_(max) is defined as equation5 described in the following.

T _(max)(dBm)=10·log 10(3.16228·10⁻⁸(mW/MHz)·BWMHz(MHz))   [Equation 5]

When regulatory requirements exist, X_(r) corresponds to a maximumenergy detection threshold defined according to the regulatoryrequirements. If the regulatory requirements do not exist, the X_(r) isconfigured by T_(max)+10 dB.

On the contrary, if the absence of the different wireless accesstechnology sharing the carrier is not guaranteed, for example, if asignal of the different wireless access technology is actually detectedin the carrier or if there is a possibility of detecting the signal, themaximum energy detection threshold (X_(Thresh) _(_) _(max)) is definedas equation 6 described in the following.

$\begin{matrix}{X_{Thresh\_ max} = {\max \begin{Bmatrix}{{{- 72}\mspace{14mu} {dB}\; m\mspace{14mu} \left( {20\mspace{14mu} {MHz}} \right)},} \\{\min \begin{Bmatrix}{T_{\max},} \\{T_{\max} - T_{A} + \left( {P_{H} - P_{TX}} \right)}\end{Bmatrix}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In equation 6, T_(A) corresponds to a constant determined according to atype of signal to be transmitted by a transmission node. When atransmission including PDSCH is performed, the T_(A) corresponds to 10dB. When a transmission including a discovery signal while PDSCH is notincluded is performed, the T_(A) corresponds to 5 dB. And, P_(H)corresponds to 23 dBm.

P_(TX) is configured by maximum transmission node (e.g., eNB) outputpower for a corresponding carrier. An eNB uses the set maximumtransmission power over a single carrier irrespective of whether singlecarrier or multi-carrier transmission is employed. For example, when aneNB intends to perform a transmission on a single carrier of 20 MHzusing 23 dBm, the P_(TX) is configured by 23 dBm. Yet, when the eNBintends to perform transmission using 20 dBm per 10 MHz channel bydividing 23 dBM into 20 dBm+20 dBm (e.g., 20 dBm transmission isperformed on one 10 MHz carrier and 20 dBm transmission is performed onanother 10 MHz carrier, CA), the P_(TX) is configured by 10 dBmcorresponding to the maximum transmit power over a single carrier.

The abovementioned energy detection threshold in LTE system correspondsto a value configured on the basis of a CCA operation on 20 MHz. Hence,it is necessary to define an energy detection threshold when atransmission node operates on 10 MHz in addition to 20 MHz.

For example, assume that LAA system coexists with WiFi and an eNBperforms 10 MHz+10 MHz CA (carrier aggregation) operation on 20 MHz bandin total. And, assume that a transmission node has transmit power of 20dBm on 10 MHz carrier (i.e., P_(TX)=20 dBm). In this case, if theaforementioned method of configuring the energy detection threshold ofLTE system is applied, an energy detection threshold can be configuredas equation 7 described in the following.

$\begin{matrix}{X_{Thresh\_ max} = {{\max \left\{ \begin{matrix}{X_{0}\mspace{14mu} {dB}\; m\mspace{11mu} \left( {10\mspace{14mu} {MH}\; z} \right)} \\{\min \begin{Bmatrix}{10\mspace{11mu} \log \mspace{11mu} 10\left( {3.16228 \cdot 10^{- 8}} \right)} \\{{10\mspace{11mu} \log \mspace{11mu} 10\mspace{11mu} \left( {3.16228 \cdot 10^{- 8}} \right)} +} \\{\left( {23 - 20} \right) \cong {{- 72}\mspace{14mu} {dB}\; m}}\end{Bmatrix}}\end{matrix} \right\}} = {\max \left\{ {{{X_{0}\left( {10\mspace{14mu} {MH}\; z} \right)}{dB}\; m},{{- 72}\mspace{14mu} {dB}\; m}} \right\}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

X₀ corresponds to a first maximum value of an energy detection thresholdwhich is defined irrespective of transmit power of an eNB on 10 MHx. Forexample, since −72 dBm is assumed on 20 MHx (e.g., equation 6), if it isdesigned to detect the same energy per unit frequency, −75 dBmcorresponding to the half of −72 dBm can be configured on 10 MHz.However, referring to equation 7, a second maximum value of the energydetection threshold, which is configured in consideration of P_(H) andP_(TX), is calculated as −72 dBm. Hence, a maximum value X_(Thresh) _(_)_(max)=max (the first maximum value, the second maximum value) of afinally induced energy detection threshold becomes −72 dBm.

Consequently, in case of 10 MHz, energy per unit frequency correspondingto a reference for detecting energy is configured to be doubled comparedto a case of 20 MHz. If X_(Thresh) _(_) _(max)=−72 dBm is satisfied notonly on 10 MHz but also on 20 MHz, energy per unit frequency on 10 MHzchannel is doubled compared to energy per unit frequency on 20 MHzchannel.

Specifically, in case of 10 MHz+10 MHz, although an eNB uses power(i.e., 20 dBm+20 dBm=23 dBm) identical to power for transmitting 23 dBmover 20 MHz, if the total detection energy for the totaled 20 MHz banddoes not exceed −69 dBm (i.e., −72 dBm+−72 dBm=−69 dBm), it may performtransmission. In particular, in case of performing 10+10 MHz CA, the eNBcan perform a more aggressive LBT compared to a case of performingsingle carrier transmission.

In particular, when the eNB performs transmission on each 10 MHz, theeNB performs the transmission with power density (e.g., power per unitfrequency) identical to power density for transmitting 23 dBm on 20 MHz.However, since equation 6 does not reflect the abovementioned fact andthe P_(TX) on 10 MHz corresponds to 20 dBm which is less than 23 dBm,adaptation is performed according to the decrease of the P_(TX). Hence,it may have such an irrational result as an energy detection thresholdwhich is increased as much as 3 dBm. In other word, although powerdensity transmitted on a single carrier is not reduced, since equation 6shows transmit power P_(TX) of an eNB in a unit of a carrier, theequation 6 determines that the P_(TX) is reduced and makes energydetection adaption to be performed.

Consequently, according to the equation 6, it may have a problem that aresult of performing LBT on a single carrier of 20 MHz is different froma result of performing LBT on 10+10 MHz CA. In other word, when atransmission node senses a single channel of 20 MHz with the sametransmit power value, it is determined that the channel is in a busystate. However, it may be determined that the channel is in an idlestate in the 10+10 MHz CA situation.

In the following, methods for solving abovementioned problem areexplained.

Proposal #8

As mentioned in the foregoing description, assume that a transmissionnode (e.g., eNB or UE) sets an energy detection threshold (or, a maximumvalue of the energy detection threshold) for a specific carrier (or, CCAbandwidth) having a arbitrary bandwidth by utilizing P_(H) or P_(TX). Inthis case, the transmission node can determine the P_(H) and/or theP_(TX) based on a bandwidth of the carrier (or, a bandwidth on which CCAis performed). For example, as the bandwidth of the carrier (or, thebandwidth on which CCA is performed) is getting wider, the transmissionnode can increase the P_(H) or decrease the P_(TX).

Specifically, a method of changing the P_(H) of equation 6 into equation8 and/or a method of changing the P_(TX) of equation 6 into equation 9are proposed.

(1) Method of changing P_(H) according to equation 8

P _(H)=23 dBm+10*log 10(BWMHz/20 MHz)   [Equation 8]

(2) Method of changing P_(TX) according to equation 9

P _(TX) =P _(TX, Carrier)+10*log 10(20 MHz/BWMHz)   [Equation 9]

In equation 9, P_(TX, Carrier) corresponds to a value of output power ofan eNB for a corresponding carrier represented in a unit of dBm. Inequations 8 and 9, BWMHz corresponds to a value of a bandwidth for acorresponding carrier represented in a unit of MHz. And, ‘log 10 ( )’corresponds to a common log with a base being 10. That is, ‘log 10(10)=1’.

The P_(H) of equation 8 and/or the P_(TX) of equation 9 may becomprehend as that increasing/decreasing the P_(H) and/or the P_(TX) byconverting a ratio between a bandwidth (e.g., BW) of an actual carrierand a reference carrier bandwidth (e.g., 20 MHz) into a unit of decibelafter configuring 20 MHz as a reference of a carrier bandwidth.

For example, in equation 8, since the P_(H) has a value of 23 dBm on thereference 20 MHz bandwidth, 23 dBm can be comprehended as referenceP_(H) power. If a bandwidth of a U-Scell in which CCA is performedcorresponds to A MHz, a transmission node adjusts the reference P_(H)power as much as a decibel value of a ratio between 20 MHz and the A MHz(e.g., 10*log 10(A/20).

Similarly, in equation 9, the P_(TX) has a value of P_(TX, Carrier) dBmon the 20 MHz bandwidth which being the reference and theP_(TX, Carrier) becomes a reference for power per carrier.

For example, if the equation 8 is applied according to the method (1),P_(H)=23 dBm+10*log 10(10/20)≈20 dBm is satisfied. Hence, a maximumvalue of an energy detection threshold on 10 MHz can be calculated asequation 11 described in the following.

$\begin{matrix}{X_{Thresh\_ max} = {{\max \left\{ \begin{matrix}{X_{0}\mspace{14mu} {dB}\; m\mspace{11mu} \left( {10\mspace{14mu} {MH}\; z} \right)} \\{\min \begin{Bmatrix}{10\mspace{11mu} \log \mspace{11mu} 10\left( {3.16228 \cdot 10^{- 8}} \right)} \\{{10\mspace{11mu} \log \mspace{11mu} 10\mspace{11mu} \left( {3.16228 \cdot 10^{- 8}} \right)} +} \\{\left( {20 - 20} \right) \cong {{- 75}\mspace{14mu} {dB}\; m}}\end{Bmatrix}}\end{matrix} \right\}} = {\max \left\{ {{{X_{0}\left( {10\mspace{14mu} {MH}\; z} \right)}{dB}\; m},{{- 75}\mspace{14mu} {dB}\; m}} \right\}}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

In particular, if X₀ is sufficiently small, a maximum value of an energydetection threshold on 10 MHz is configured as −75 dBm. Hence, it may beable to identically configure an energy level per unit frequency for acase of −72 dBm which is the maximum value of the energy detectionthreshold for 20 MHz and a case of −75 dBm which is the maximum value ofthe energy detection threshold for 10 MHz.

Or, as shown in equation 12, a transmission node can decrease a T_(A)value as a bandwidth of a carrier (or, CCA bandwidth) is getting wider.Or, as shown in equation 13, the transmission node can adopt, as aseparate variable, a T_(B) value which is increased as a bandwidth isgetting wider.

(3) Method of changing T_(A) according to equation 12

T _(A) =T _(A, old)+10*log 10(20 MHz/BWMHz)   [Equation 12]

T_(A) _(_) _(old) corresponds to a value irrespective of a carrierbandwidth (or, CCA bandwidth). The T_(A) _(_) _(old) corresponds to aconstant determined according to a type of a signal to be transmitted bya transmission node. If the transmission node corresponds to an eNB, fora transmission including PDSCH, the T_(A) corresponds to 10 dB, and fora transmission including a discovery signal and excluding PDSCH, theT_(A) corresponds to 5 dB. If the transmission node corresponds to a UE,the T_(A) is configured as 10 dB for the transmission of PUSCH and theT_(A) is configured as 5 dB for the transmissio of PUCCH or PRACH, bywhich the present invention may be non-limited.

(4) Method of adopting T_(B)

T _(B)=10*log 10(BWMHz/20 MHz)   [Equation 13]

In equation 13, a method of applying a newly defined T_(B) can be moresegmented. For example, a maximum value (X_(Threshold) _(_) _(max)) ofan energy detection threshold can be simply represented as ‘max {EQ_B,min (T_(max), EQ_A)}’. EQ_A corresponds to an equation for calculatingan energy detection threshold (or, a maximum value of an energydetection threshold) in consideration of P_(H) and P_(TX) and EQ_Bcorresponds to an equation for calculating an energy detection threshold(or, a maximum value of an energy detection threshold) withoutconsidering P_(H) and P_(TX). For example, in case of the equation 6,since the EQ_B has a constant value of −72 dBm and the EQ_B makes amaximum value of an energy detection threshold (X_(Threshold) _(_)_(max)) to be equal to or greater than −72 dBm, it may be able tocomprehend the EQ_B as an equation for defining a lower bound of themaximum value of the energy detection threshold.

The T_(B) defined in equation 13 can be applied to either the EQ_A orthe EQ_B only. Or, the T_(B) can be applied to both the EQ_A and theEQ_B. Equations 14 to 17 illustrate various examples to which the T_(B)is applied.

(i) In case that T_(B) is applied to EQ_A only,

$\begin{matrix}{X_{Thresh\_ max} = {\max \begin{Bmatrix}{{- 72}\mspace{14mu} {dB}\; m} \\{\min \begin{Bmatrix}T_{m\; {ax}} \\{T_{\max} - T_{A} + T_{B} + \left( {P_{H} - P_{TX}} \right)}\end{Bmatrix}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

(ii) In case that T_(B) is applied to both EQ_A and EQ_B,

$\begin{matrix}{X_{Thresh\_ max} = {\max \begin{Bmatrix}{{{- 72}\mspace{14mu} {dB}\; m} + T_{B}} \\{\min \begin{Bmatrix}T_{m\; {ax}} \\{T_{\max} - T_{A} + T_{B} + \left( {P_{H} - P_{TX}} \right)}\end{Bmatrix}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

(iii) When EQ_B corresponds to a function of a bandwidth and T_(B) isapplied to EQ_A only,

$\begin{matrix}{X_{Thresh\_ max} = {\max \begin{Bmatrix}{T_{\max} - T_{A}} \\{\min \begin{Bmatrix}T_{\max} \\{T_{m\; {ax}} - T_{A} + T_{B} + \left( {P_{H} - P_{TX}} \right)}\end{Bmatrix}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

(iv) When EQ_B corresponds to a function of a bandwidth and T_(B) isapplied to both EQ_A and EQ_B,

$\begin{matrix}{X_{Thresh\_ max} = {\max \left\{ \; \begin{matrix}{T_{m\; {ax}} - T_{A} + T_{B}} \\{\min \begin{Bmatrix}T_{m\; {ax}} \\{T_{m\; {ax}} - T_{A} + T_{B} + \left( {P_{H} - P_{TX}} \right)}\end{Bmatrix}}\end{matrix} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

In the equations 14 to 17, T_(A) corresponds to a value determinedirrespective of a carrier bandwidth (or, CCA bandwidth). The T_(A)corresponds to a constant determined according to a type of a signal tobe transmitted by a transmission node. If the transmission nodecorresponds to an eNB, the T_(A) corresponds to 10 dB for a transmissionincluding PDSCH and the T_(A) corresponds to 5 dB for a transmissionincluding a discovery signal but excluding PDSCH. If the transmissionnode corresponds to a UE, the T_(A) is configured as 10 dB to transmitPUSCH and the T_(A) is configured as 5 dB to transmit PUCCH or PRACH, bywhich the present invention may be non-limited.

P_(H) corresponds to 23 dBm.

P_(TX) is configured as maximum transmission node (e.g., eNB) outputpower for a corresponding carrier. An eNB uses the set maximumtransmission power over a single carrier irrespective of whether singlecarrier or multi-carrier transmission is employed.

For T_(max), it may refer to equation 5.

The equation 15 according to (ii) of the method (4) can be summarized asequation 18 described in the following.

$\begin{matrix}{X_{Thresh\_ max} = {\max \begin{Bmatrix}{{{- 72} + {{10 \cdot \log}\; 10\; \left( {{BW}\mspace{14mu} {{MHz}/20}\mspace{14mu} {MHz}} \right)\mspace{11mu} {dB}\; m}},} \\{\min \begin{Bmatrix}{T_{\max},} \\\begin{matrix}{T_{\max} - T_{A} + \left( {P_{H} + {10 \cdot}} \right.} \\\left. {{\log \; 10\left( {{BW}\mspace{14mu} {{MHz}/20}\mspace{14mu} {MHz}} \right)} - P_{TX}} \right)\end{matrix}\end{Bmatrix}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$

FIG. 18 is a flowchart for explaining a method of configuring a maximumvalue of an energy detection threshold according to one embodiment ofthe present invention. For example, FIG. 18 is based on (ii) of themethod (4). Explanation on contents overlapped with the aforementionedcontent can be omitted.

Assume that a transmission node (e.g., eNB or UE) performs CCA on LAAScell. In order to perform the CCA, the transmission node determines anenergy detection threshold. In this case, the energy detection thresholdshould be configured as a value equal to or less than a maximum valuedetermined according to the aforementioned embodiments. Thus, thetransmission node has to firstly determine the maximum value of theenergy detection threshold.

If an absence of a different technology (e.g., WiFi, etc.) sharing acarrier (e.g., LAA Scell) is not guaranteed, a maximum value of anenergy detection threshold according to the embodiments of the presentinvention can be determined based on a value (i.e., T_(B)) of a ratiobetween a reference bandwidth size (e.g., 20 MHz) and an actualbandwidth of LAA Scell in which CCA is performed by a transmission node.

First of all, the transmission node determines whether or not an absenceof a different technology (e.g., radio access technology (RAT)) sharinga corresponding carrier (e.g., LAA Scell) can be guaranteed in a longterm basis [S1805]. In particular, although a signal (e.g., WiFi) of adifferent RAT is not detected on a corresponding carrier during arelatively short period (e.g., short term), the transmission node isunable to determine it as the carrier is not shared by the differentRAT. It is necessary for the transmission node to determine whether ornot the absence of the different RAT exists on a long term basis. A timelength corresponding to the long term can be determined in advance basedon regulations for LAA Cell band, by which the present invention may benon-limited.

If an absence of a different technology sharing a corresponding carrier(e.g., a carrier on which LAA Scell is located) is guaranteed, thetransmission node determines a maximum value of an energy detectionthreshold based on equation 4 [S1810].

On the contrary, if the absence of the different technology sharing acorresponding carrier (e.g., LAA Scell) is not guaranteed, thetransmission node determines T_(B) based on equation 13 [S1815].

The transmission node calculates EQ_A and EQ_B based on the T_(B)[S1820]. For example, referring to equation 15, the EQ_A corresponds toT_(max)−T_(A)+(P_(H)+T_(B)−P_(TX)) and the EQ_B corresponds to−72+T_(B). The T_(max) is calculated by equation 5 and P_(H) correspondsto 23 dBm. The P_(TX) corresponds to transmit power. For the T_(A), itmay refer to the aforementioned description.

The transmission node compares the T_(max) with the EQ_A [S1825]. Thetransmission node selects a smaller value from among the T_(max) and theEQ_A and compares the selected value with the EQ_B.

If the T_(max) is equal to or greater than the EQ_A, the transmissionnode compares the EQ_A with the EQ_B [S1830]. If the EQ_A is equal to orgreater than the EQ_B, the transmission node configures the maximumvalue of the energy detection threshold as the EQ_A [S1835]. On thecontrary, if the EQ_A is less than the EQ_B, the transmission nodeconfigures the maximum value of the energy detection threshold as theEQ_B [S1840].

Meanwhile, in the step S1825, if the EQ_A is greater than the T_(max),the transmission node compares the T_(max) with the EQ_B [S1845]. If theT_(max) is equal to or greater than the EQ_B, the transmission nodeconfigures the maximum value of the energy detection threshold as theT_(max) [S1850]. On the contrary, if the EQ_B is greater than theT_(max), the transmission node configures the maximum value of theenergy detection threshold as the EQ_B [S1840].

If the maximum value of the energy detection threshold is configured,the transmission node determines an energy detection threshold within arange not exceeding the maximum value of the energy detection threshold.The transmission node compares energy (e.g., power) of a signal detectedby performing CCA on LAA Scell, with the determined energy detectionthreshold, and determine whether or not it is able to perform atransmission for the LAA Scell. In particular, the transmission nodedetermines whether the LAA Scell is in an idle state or a busy state. Ifthe LAA Scell is in the idle state, the transmission node performssignal transmission for the LAA Scell. If the LAA Scell is in the busystate, the transmission node defers the signal transmission for the LAAScell.

Proposal #9

If a transmission node performs CCA in a bandwidth narrower than areference bandwidth (e.g., 20 MHz), it may apply a penalty (or,encourage) value in proportion to a bandwidth of an energy detectionthreshold (or, a maximum value of the energy detection threshold),

According to the method of configuring an energy detection threshold (amaximum value of the energy detection threshold) mentioned earlier inthe proposal #8, although a bandwidth is changed, detection energy perunit frequency, which is configured on the basis of 20 MHz, isidentically maintained.

Meanwhile, in environment in which an interference cell exists, among 20MHz band capable of being divided into two 10 MHz bands, assume that theinterference cell performs a transmission with signal strength (TXP1)greater than the half (e.g., −75 dBm) of −72 dBm on the first 10 MHzband and performs a transmission with signal strength (TXP2) less thanthe half of −72 dBm on the second 10 MHz band. For clarity, assume thatTXP1+TXP2=−72 dBm is satisfied.

In the example above, since an eNB 1 performing CCA in a unit of 20 MHzdetects −72 dBm on the entire 20 MHz band, the eNB 1 defers signaltransmission on the entire 20 MHz band including the second 10 MHz band.On the contrary, since an eNB 2 performing CCA in a unit of 10 MHzdetects signal strength less than −75 dBm on the second 10 MHz band, theeNB 2 can perform signal transmission.

According to one embodiment of the present invention, if CCA isperformed on a bandwidth narrower than a reference bandwidth (e.g., 20MHz), it may apply a penalty value to the energy detection threshold(or, the maximum value of the energy detection threshold) inconsideration of an equity problem. In case of applying the penaltyvalue, it may indicate that a prescribed value is subtracted from theenergy detection threshold (or, the maximum value of the energydetection threshold), by which the present invention may be non-limited.The penalty value can be configured by a constant or can be configuredin proportion to a CCA bandwidth.

On the contrary, when a CCA bandwidth is narrow, if interference is notevenly received on the whole band, channel access occasion can bereduced. Hence, it may apply an encourage value to the energy detectionthreshold (or, the maximum value of the energy detection threshold). Incase of applying the encourage value, it may indicate that a prescribedvalue is added to the energy detection threshold (or, the maximum valueof the energy detection threshold), by which the present invention maybe non-limited. The encourage value can be configured by a constant orcan be configured in proportion to a CCA bandwidth.

The penalty value or the encourage value can be reflected to a value ofthe T_(A) in the equation 6.

Proposal #10

According to one embodiment of the present invention, it may be able todefine an energy detection threshold (or, a maximum value of the energydetection threshold) for performing CCA in advance for the M number {N₁,N₂, . . . , N_(M)} of bandwidths. When a bandwidth on which a signal isto be transmitted corresponds to L, a transmission node can perform CCAon a narrowest bandwidth among bandwidths having a value equal to orgreater than the L (or, a widest bandwidth among bandwidths having avalue equal to or less than the L).

For example, if a separate energy detection threshold for 10 MHz LAAsystem is not defined, an energy detection threshold for 20 MHz band canbe reused.

In more general, if an energy detection threshold for partial referencebandwidths (e.g., M number of bandwidths) is defined, a transmissionnode selects a narrowest reference bandwidth including a bandwidth onwhich a signal is to be transmitted and can perform CCA based on anenergy detection threshold for the selected bandwidth.

Proposal #11

A transmission for LAA SCell may correspond to DL transmission of an eNBor UL transmission of a UE. When the UE performs a UL LBT operation, itmay be able to define a priority for channels in the aspect of an energydetection threshold. If a channel has a higher priority, a maximum valueof an energy detection threshold can be configured to be a greatervalue.

For example, regarding the energy detection threshold, priorities can beset to channels as follows.

PRACH>PUCCH>PUSCH with UCI piggyback>PUSCH without UCI (=PUSCH withSRS)>SRS only

If LAA U-band supports UL channel transmission, a transmissionprobability of a UL channel on which relatively important informationsuch as random access, UCI, or the like is transmitted can be degradedor transmission can be delayed due to LBT-based transmission of theU-band. Consequently, reliability can be reduced.

In order to solve the problem above, when a UL channel on which randomaccess or UCI is transmitted is transmitted, it may be able to configurechannel access possibility of the UL channel to be higher compared to acase that a UL LBT operation is performed on a different generalchannel. As a method of increasing the channel access possibility, aneNB can indicate a relatively higher energy detection threshold to beconfigured for a UL channel including a random access channel or UCIwhen a UE performs UL LBT. If the relatively higher energy detectionthreshold is configured, it is highly probable that a channel isdetermined as idle.

Meanwhile, referring to 6.2.5 Configured transmitted power of 3GPP TS36.101, an LTE UE (e.g., UE) reflects maximum power indicated by an eNB(or, network), a power class of the UE, MPR (maximum power reduction) inconsideration of PAPR(Peak-to-Average Power Ratio), A-MPR (additionalmaximum power reduction), P-MPR (power management term for MPR),Tolerance, and the like to determine (Configured maximum power)P_(CMAX,c) of the LTE UE.

Specifically, a UE configures a maximum power value P_(CMAX,c) of the UEfor a serving cell c to satisfy P_(CMAX) _(_) _(L,c)≤P_(CMAX,c)≤P_(CMAX)_(_) _(H,c).

The P_(CMAX) _(_) _(L,c) and the P_(CMAX) _(_) _(H,c) are defined asequation 19 described in the following.

P _(CMAX) _(—L,c) =MIN {P _(EMAX,c) −T _(C,c) , P_(PowerClass)−MAX(MPR_(c)+A-MPR_(c) +ΔT _(IB,c) +T _(C,c) +T _(Prose),P-MPR_(c))}P _(CMAX) _(_) _(H,c)=MIN {P _(EMAX,c) , P_(PowerClass)}  [Equation 19]

In equation 19, P_(EMAX,c) corresponds to a value given via RRCsignaling for a serving cell C. P_(PowerClass) corresponds to maximum UEpower not considering tolerance. MPR_(c) and A-MPR_(c) correspond tomaximum power reduction and additional maximum power reduction,respectively, for the serving cell C. ΔT_(IB,c) corresponds toadditional tolerance for the serving cell C. ΔT_(c,c) is configured by1.5 dB or 0 dB. ΔT_(ProSe) is configured by 0.1 dB or 0 dB depending onwhether or not a UE supports D2D communication. P-MPR_(c) corresponds topermitted maximum output power reduction. For more details of theabovementioned parameters, it may refer to 6.2.5 of 3GPP TS 36.101.

Meanwhile, if the UE determines an energy detection threshold for a ULLBT operation via at least one selected from among the aforementionedproposals 8 to 10, it may use P_(CMAX,c) instead of P_(TX). In moregeneral, values described in the following can be used instead of aP_(TX) value of a UE (hereinafter, P_(TX, UE)).

Proposal #12

In case of performing a UL LBT, it may use P_(TX, UE) described in thefollowing instead of the P_(TX) of the equation 6.

P _(TX, UE) =P _(CMAX) _(_) _(H,c)=MIN {P _(EMAX,c) , P_(PowerClass)}  (1)

P _(TX, UE) =P _(EMAX,c)   (2)

P _(TX, UE)=MIN {P _(EMAX,c) −ΔT _(C,c) , P _(PowerClass)−(ΔT _(IB,c)+ΔT _(C,c) +ΔT _(Prose))}  (3)

For example, if it is assumed that a UE determines an energy detectionthreshold based on the equation 6 in a UL LBT process, it may be able touse P_(CMAX,c) as a P_(TX,UE) value instead of P_(TX). In this case, inorder to make the P_(TX,UE) value have static characteristic, the UEconsiders MPR only in determining the P_(CMAX,c). Or, the UE may excludeMPR (e.g., A-MPR) which varies according to a modulation order, TX RB,or the like. Or, the UE may reflect A-MPR only that assumes a highestmodulation order and RB allocation of a maximum BW.

The aforementioned proposals can be applied not only to DL LBT but alsoto UL LBT.

Indexes assigned to the aforementioned proposals are assigned forclarity of explanation. It is not mandatory that proposals having adifferent index configure an independent embodiment. In particular,although it is able to individually implement each of the proposalshaving a different index, the proposals can be implemented as a singleinvention in a manner of being combined with each other.

FIG. 19 a flowchart for a method of performing channel access accordingto one embodiment of the present invention. Explanation on contentsoverlapped with the aforementioned content can be omitted.

Referring to FIG. 19, a transmission node (e.g., base station)determines a maximum energy detection threshold [S1905]. The maximumenergy detection threshold corresponds to a maximum value of an energydetection threshold for performing CCA. The transmission node configuresthe energy detection threshold to be equal to or less than the maximumenergy detection threshold [S1910].

The transmission node senses a carrier of an unlicensed band [S1915].For example, a base station can sense a carrier where an LAA SCell viawhich a downlink signal to be transmitted by the base station, resides.

The transmission node can determine whether the carrier is in an idlestate or a busy state by comparing the energy detection threshold withpower which is detected as a result of the carrier sensing [S1920].

If the power detected as the result of the carrier sensing is less thanthe energy detection threshold, the transmission node transmits a signalvia the LAA SCell [S1925]. If the detected power is equal to or greaterthan the energy detection threshold, the transmission node defers signaltransmission [S1930]. If the signal transmission is deferred, thetransmission node sets a timer for deferring channel access and may beable to perform CCA after the timer expires.

Meanwhile, if a different radio access technology (RAT) sharing acarrier is able to exist, the maximum energy detection threshold can bedetermined adaptively to a bandwidth of a carrier using a decibel value(e.g., T_(B) of equation 13) of a ratio between a reference bandwidthand the bandwidth of the carrier.

The maximum energy detection threshold can be configured by a valueequal to or greater than a first power value which is a sum of a lowerbound of a maximum energy detection threshold for the referencebandwidth and the decibel value (e.g., T_(B) of equation 13). The firstpower value can be obtained by a first equation (e.g., EQ_B of FIG. 18)‘−72+10*log 10(BWMHz/20 MHz) [dBm]’. In the first equation, ‘20 MHz’corresponds to a reference bandwidth, ‘BWMHz’ corresponds to a bandwidthof a carrier represented in a unit of MHz, ‘10*log 10(BWMHz/20 MHz)’corresponds to a decibel value (e.g., T_(B) of equation 13), and ‘−72’corresponds to a lower bound of the maximum energy detection thresholdfor the reference bandwidth represented in a unit of dBm.

The maximum energy detection threshold can be configured by a valueequal to or greater than a second power value which is determined inconsideration of a difference between the decibel value (e.g., T_(B) ofequation 13) and the maximum energy detection threshold of thetransmission node configured for the carrier. The second power value canbe obtained by a second equation ‘min {T_(max),T_(max)−T_(A)+(P_(H)+10*log 10(BWMHz/20 MHz)−P_(TX))} [dBm]’. In thesecond equation, ‘T_(max)’corresponds to ‘10*log10(3.16288*10⁻⁸/BWMHz)’, ‘T_(A)’ corresponds to a constant predefinedaccording to a type of the downlink signal, and ‘P_(TX)’ may correspondto maximum transmit power of the transmission node configured for thecarrier. If a downlink signal includes physical downlink shared channel(PDSCH), ‘T_(A)’ is configured as 10 dB. If the downlink signal includesa discovery signal and does not include PDSCH, ‘T_(A)’ can be configuredas 5 dB.

And, the maximum energy detection threshold can be determined to be agreater value among a first power value obtained by adding a decibelvalue to −72 dBm and a second power value.

If a different RAT sharing a carrier does not exist, the maximum energydetection threshold may not exceed T_(max)+10 dB.

FIG. 20 is a block diagram illustrating a base station (BS) 105 and auser equipment (UE) 110 for use in a wireless communication system 100according to the present invention. The BS and the UE of FIG. 20 mayperform the operations of aforementioned embodiments.

Referring to FIG. 20, the BS 105 may include a transmission (Tx) dataprocessor 115, a symbol modulator 120, a transmitter 125, atransmission/reception antenna 130, a processor 180, a memory 185, areceiver 190, a symbol demodulator 195, and a reception (Rx) dataprocessor 197. The UE 110 may include a Tx data processor 165, a symbolmodulator 170, a transmitter 175, a transmission/reception antenna 135,a processor 155, a memory 160, a receiver 140, a symbol demodulator 155,and an Rx data processor 150. In FIG. 12, although one antenna 130 isused for the BS 105 and one antenna 135 is used for the UE 110, each ofthe BS 105 and the UE 110 may also include a plurality of antennas asnecessary. Therefore, the BS 105 and the UE 110 according to the presentinvention support a Multiple Input Multiple Output (MIMO) system. The BS105 according to the present invention can support both a SingleUser-MIMO (SU-MIMO) scheme and a Multi User-MIMO (MU-MIMO) scheme.

In downlink, the Tx data processor 115 receives traffic data, formatsthe received traffic data, codes the formatted traffic data, interleavesthe coded traffic data, and modulates the interleaved data (or performssymbol mapping upon the interleaved data), such that it providesmodulation symbols (i.e., data symbols). The symbol modulator 120receives and processes the data symbols and pilot symbols, such that itprovides a stream of symbols.

The symbol modulator 120 multiplexes data and pilot symbols, andtransmits the multiplexed data and pilot symbols to the transmitter 125.In this case, each transmission (Tx) symbol may be a data symbol, apilot symbol, or a value of a zero signal (null signal). In each symbolperiod, pilot symbols may be successively transmitted during each symbolperiod. The pilot symbols may be an FDM symbol, an OFDM symbol, a TimeDivision Multiplexing (TDM) symbol, or a Code Division Multiplexing(CDM) symbol.

The transmitter 125 receives a stream of symbols, converts the receivedsymbols into one or more analog signals, and additionally adjusts theone or more analog signals (e.g., amplification, filtering, andfrequency upconversion of the analog signals), such that it generates adownlink signal appropriate for data transmission through an RF channel.Subsequently, the downlink signal is transmitted to the UE through theantenna 130.

Configuration of the UE 110 will hereinafter be described in detail. Theantenna 135 of the UE 110 receives a DL signal from the BS 105, andtransmits the DL signal to the receiver 140. The receiver 140 performsadjustment (e.g., filtering, amplification, and frequencydownconversion) of the received DL signal, and digitizes the adjustedsignal to obtain samples. The symbol demodulator 145 demodulates thereceived pilot symbols, and provides the demodulated result to theprocessor 155 to perform channel estimation.

The symbol demodulator 145 receives a frequency response estimationvalue for downlink from the processor 155, demodulates the received datasymbols, obtains data symbol estimation values (indicating estimationvalues of the transmitted data symbols), and provides the data symbolestimation values to the Rx data processor 150. The Rx data processor150 performs demodulation (i.e., symbol-demapping) of data symbolestimation values, deinterleaves the demodulated result, decodes thedeinterleaved result, and recovers the transmitted traffic data.

The processing of the symbol demodulator 145 and the Rx data processor150 is complementary to that of the symbol modulator 120 and the Tx dataprocessor 115 in the BS 205.

The Tx data processor 165 of the UE 110 processes traffic data inuplink, and provides data symbols. The symbol modulator 170 receives andmultiplexes data symbols, and modulates the multiplexed data symbols,such that it can provide a stream of symbols to the transmitter 175. Thetransmitter 175 receives and processes the stream of symbols to generatean uplink (UL) signal, and the UL signal is transmitted to the BS 105through the antenna 135.

The BS 105 receives the UL signal from the UE 110 through the antenna130. The receiver processes the received UL signal to obtain samples.Subsequently, the symbol demodulator 195 processes the symbols, andprovides pilot symbols and data symbol estimation values received viauplink. The Rx data processor 197 processes the data symbol estimationvalue, and recovers traffic data received from the UE 110.

A processor 155 or 180 of the UE 110 or the BS 105 commands or indicatesoperations of the UE 110 or the BS 105. For example, the processor 155or 180 of the UE 110 or the BS 105 controls, adjusts, and managesoperations of the UE 210 or the BS 105. Each processor 155 or 180 may beconnected to a memory unit 160 or 185 for storing program code and data.The memory 160 or 185 is connected to the processor 155 or 180, suchthat it can store the operating system, applications, and general files.

The processor 155 or 180 may also be referred to as a controller, amicrocontroller), a microprocessor, a microcomputer, etc. In themeantime, the processor 155 or 180 may be implemented by various means,for example, hardware, firmware, software, or a combination thereof. Ina hardware configuration, methods according to the embodiments of thepresent invention may be implemented by the processor 155 or 180, forexample, one or more application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

In a firmware or software configuration, methods according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. which perform the above-describedfunctions or operations. Firmware or software implemented in the presentinvention may be contained in the processor 155 or 180 or the memoryunit 160 or 185, such that it can be driven by the processor 155 or 180.

Radio interface protocol layers among the UE 110, the BS 105, and awireless communication system (i.e., network) can be classified into afirst layer (L1 layer), a second layer (L2 layer) and a third layer (L3layer) on the basis of the lower three layers of the Open SystemInterconnection (OSI) reference model widely known in communicationsystems. A physical layer belonging to the first layer (L1) provides aninformation transfer service through a physical channel. A RadioResource Control (RRC) layer belonging to the third layer (L3) controlsradio resources between the UE and the network. The UE 110 and the BS105 may exchange RRC messages with each other through the wirelesscommunication network and the RRC layer.

In the present specification, although the processor 155 of the UE andthe processor 180 of the BS perform an operation of processing a signaland data except a function of receiving a signal, a function oftransmitting a signal, and a storing function performed by the UE 110and the BS 105, for clarity, the processor 155/180 is not specificallymentioned in the following description. Although the processor 155/180is not specifically mentioned, it may assume that the processor performsa series of operations such as data processing and the like rather thanthe function of receiving a signal, the function of transmitting asignal, and the storing function.

According to one embodiment of the present invention, a processor of anbase station senses a carrier of an unlicensed band for transmitting adownlink signal. If power detected by sensing the carrier is less thanan energy detection threshold configured by the base station, atransmitter transmits the downlink signal. The energy detectionthreshold can be configured to be equal to or less than a maximum energydetection threshold determined by the base station. If a different radioaccess technology (RAT) sharing the carrier is able to exist, themaximum energy detection threshold can be determined adaptively to abandwidth of the carrier using a decibel value of a ratio between areference bandwidth and the bandwidth of the carrier.

The above-mentioned embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, it isable to consider that the respective elements or features are selectiveunless they are explicitly mentioned. Each of the elements or featurescan be implemented in a form failing to be combined with other elementsor features. Moreover, it is able to implement an embodiment of thepresent invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment. And, it is apparently understandable that an embodiment isconfigured by combining claims failing to have relation of explicitcitation in the appended claims together or can be included as newclaims by amendment after filing an application.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention can be applied to variouswireless communication systems including 3GPP based wirelesscommunication system.

1. A method of performing channel access on an unlicensed band by a basestation in a wireless communication system, the method comprising:sensing a carrier of an unlicensed band for transmitting a downlinksignal; and transmitting the downlink signal when power detected bysensing the carrier is less than an energy detection threshold that isconfigured by the base station, wherein the energy detection thresholdis configured to be equal to or less than a maximum energy detectionthreshold determined by the base station and wherein when a differentradio access technology (RAT) sharing the carrier is able to exist, themaximum energy detection threshold is determined adaptively to abandwidth of the carrier using a decibel value of a ratio between areference bandwidth and the bandwidth of the carrier.
 2. The method ofclaim 1, wherein the maximum energy detection threshold is configured tobe equal to or greater than a first power value which is a sum of alower bound of the maximum energy detection threshold for the referencebandwidth and the decibel value.
 3. The method of claim 2, wherein thefirst power value is obtained by a first equation ‘−72+10*log10(BWMHz/20 MHz) [dBm]’, where ‘20 MHz’ of the first equationcorresponds to the reference bandwidth, ‘BWMHz’ corresponds to thebandwidth of the carrier represented in a unit of MHz, ‘10*log10(BWMHz/20 MHz)’ corresponds to the decibel value, and ‘−72’corresponds to the lower bound of the maximum energy detection thresholdfor the reference bandwidth represented in a unit of dBm.
 4. The methodof claim 1, wherein the maximum energy detection threshold is configuredto be equal to or greater than a second power value which is determinedin consideration of a difference between the decibel value and maximumtransmit power of the base station set for the carrier.
 5. The method ofclaim 4, wherein the second power value is obtained by a second equation‘min {T_(max), T_(max)−T_(A)+(P_(H)+10*log 10(BWMHz/20 MHz)−P_(TX))}[dBm]’, where ‘T_(max)’ of the second equation corresponds to ‘10*log10(3.16288*10⁻⁸/BWMHz)’, ‘T_(A)’ corresponds to a constant predefinedaccording to a type of the downlink signal, ‘P_(H)’ corresponds to 23dBm, ‘20 MHz’ corresponds to the reference bandwidth, ‘BWMHz’corresponds to the bandwidth of the carrier represented in a unit ofMHz, ‘10*log 10(BWMHz/20 MHz)’ corresponds to the decibel value, and‘P_(TX)’ corresponds to the maximum transmit power of the base stationset for the carrier.
 6. The method of claim 5, wherein the maximumenergy detection threshold is determined to be a greater value among thefirst power value obtained by adding the decibel value to −72 dBm andthe second power value.
 7. The method of claim 5, wherein when thedownlink signal contains a physical downlink shared channel (PDSCH), the‘T_(A)’ is configured as 10 dB and wherein when the downlink signalcontains a discovery signal but does not contain the PDSCH, the ‘T_(A)’is configured as 5 dB.
 8. The method of claim 5, wherein when thedifferent RAT sharing the carrier does not exist, the maximum energydetection threshold does not exceed T_(max)+10 dB.
 9. The method ofclaim 1, wherein the downlink signal is transmitted via at least onelicensed-assisted access secondary cell (LAA SCell) operating based onLAA and wherein the sensed carrier corresponds to a carrier at which theat least one LAA SCell resides.
 10. A base station performing channelaccess on an unlicensed band, the base station comprising: a processorto sense a carrier of an unlicensed band for transmitting a downlinksignal; and a transmitter to transmit the downlink signal when powerdetected by sensing the carrier is less than an energy detectionthreshold that is configured by the base station, wherein the energydetection threshold is configured to be equal to or less than a maximumenergy detection threshold determined by the base station and whereinwhen a different radio access technology (RAT) sharing the carrier isable to exist, the maximum energy detection threshold is determinedadaptively a bandwidth of the carrier using a decibel value of a ratiobetween a reference bandwidth and the bandwidth of the carrier.
 11. Thebase station of claim 10, wherein the maximum energy detection thresholdis configured to be equal to or greater than a first power value whichis a sum of a lower bound of the maximum energy detection threshold forthe reference bandwidth and the decibel value.
 12. The base station ofclaim 11, wherein the first power value is obtained by a first equation‘−72+10*log 10(BWMHz/20 MHz) [dBm]’, where ‘20 MHz’ of the firstequation corresponds to the reference bandwidth, ‘BWMHz’ corresponds tothe bandwidth of the carrier represented in a unit of MHz, ‘10*log10(BWMHz/20 MHz)’ corresponds to the decibel value, and ‘−72’corresponds to the lower bound of the maximum energy detection thresholdfor the reference bandwidth represented in a unit of dBm.
 13. The basestation of claim 10, wherein the maximum energy detection threshold isconfigured to be equal to or greater than a second power value which isdetermined in consideration of a difference between the decibel valueand maximum transmit power of the base station set for the carrier. 14.The base station of claim 13, wherein the second power value is obtainedby a second equation ‘min {T_(max), T_(max)−T_(A)+(P_(H)+10*log10(BWMHz/20 MHz)−P_(TX))} [dBm]’, wherein ‘T_(max)’ of the secondequation corresponds to ‘10*log 10(3.16288*10⁻⁸/BWMHz)’, where ‘T_(A)’corresponds to a constant predefined according to a type of the downlinksignal, ‘P_(H)’ corresponds to 23 dBm, ‘20 MHz’ corresponds to thereference bandwidth, ‘BWMHz’ corresponds to the bandwidth of the carrierrepresented in a unit of MHz, ‘10*log 10(BWMHz/20 MHz)’ corresponds tothe decibel value, and ‘P_(TX)’ corresponds to the maximum transmitpower of the base station set for the carrier.
 15. The base station ofclaim 14, wherein the maximum energy detection threshold is determinedto be a greater value among the first power value obtained by adding thedecibel value to −72 dBm and the second power value.
 16. The method ofclaim 2, wherein the maximum energy detection threshold is configured tobe equal to or greater than a second power value which is determined inconsideration of a difference between the decibel value and maximumtransmit power of the base station set for the carrier.
 17. The methodof claim 3, wherein the maximum energy detection threshold is configuredto be equal to or greater than a second power value which is determinedin consideration of a difference between the decibel value and maximumtransmit power of the base station set for the carrier.
 18. The basestation of claim 11, wherein the maximum energy detection threshold isconfigured to be equal to or greater than a second power value which isdetermined in consideration of a difference between the decibel valueand maximum transmit power of the base station set for the carrier. 19.The base station of claim 12, wherein the maximum energy detectionthreshold is configured to be equal to or greater than a second powervalue which is determined in consideration of a difference between thedecibel value and maximum transmit power of the base station set for thecarrier.